I. Canon Law

It may be useful first to outline the main elements of just war theory in canon law, to contrast medieval Roman and canon law on war, and indicate some of their mutual influence. Saint Augustine of Hippo (354–430), who is generally considered the founder of the just war tradition, made comments on war in a few works, which reflect a set of attitudes rather than a systematic theory.Footnote ⁶ In describing just wars, Augustine included both secular and religious elements. Relying on a definition likely derived from Roman legal sources, he wrote that just wars avenged or punished injuries (injuriae: any wrongs done to another), after one people or nation had failed to restore what they had taken unjustly, or failed to rectify something they had done illicitly to another nation.Footnote ⁷ According to Augustine, these just wars could only be taken up by a legitimate public authority. In a more religious vein, he accepted that wars waged on God's authority, to humble those who offended Him, were naturally just.Footnote ⁸ Although Augustine saw that only necessary wars should be undertaken, and only for the sake of peace, war had an important dimension of divinely guided punishment and correction for sin. For Augustine, soldiers and their leaders were to wage war with virtuous intentions, but obedience was the soldier's main duty.Footnote ⁹ The soldier was guiltless in the execution of unjust commands, although able to resist orders that directly contravened divine precepts.Footnote ¹⁰ With his few and fairly scattered comments, Augustine came to stand at the head of the medieval just war tradition.

Canon law adopted Augustine's views on war through Gratian's Decretum, the landmark collection of law in circulation by the mid-twelfth century. The tradition of war that developed in the Decretum and its glossators, the Decretists, is nuanced, but evolved within Gratian's framework.Footnote ¹¹ The Decretist Rufinus (fl. 1150–91), as an example of the tradition, viewed war as a way to repel unjust injuries immediately or to inflict punishment for prior injuries.Footnote ¹² No clear line was drawn in Decretist thought between these kinds of wars, although the view that any just war was based on justified defense was common.Footnote ¹³ Decretists also shared an assumption that justice in war operated on one side only, with the result that the unjust side defended itself unjustly.Footnote ¹⁴ The unjust side was thought to merit the war waged against it, on account of an offense or a moral fault, and was to restore taken or violated goods or rights, and to accept just punishment rather than contumaciously resist.Footnote ¹⁵ Although normally, medieval jurists considered individual self-defense to be a natural right, the limitation of war to those who waged it justly fit well with an objective view of justice and an overriding canonistic concern for war guided by moral authority.Footnote ¹⁶ The notion of war as moral punishment and correction also bore similarities to the canonistic treatment of heretics, who were likewise to accept correction.Footnote ¹⁷ For Gratian and his successors, the just side had a thoroughgoing moral and legal authority over the unjust side, although punishment was not to exceed the offense or fault.Footnote ¹⁸ By the time the canonist Raymond of Penafort (c. 1180–1275) treated the just war, it included the criteria that would become familiar in the definition of Thomas Aquinas (1225–74): proper authority for war, a just cause, and the right intention.Footnote ¹⁹

In the thirteenth century, jurists who commented on a new, official collection of canon law, the Decretals of Gregory IX, sometimes took a more pragmatic approach. This was partly because of the more specific legal questions they confronted in their texts. In particular, the commentary of Pope Innocent IV (c. 1195–1254) had an influence on civilian analyses of war, as well as subsequent canon law, and he based his arguments fairly extensively on Roman law. As a canonist, Innocent was comfortable with topics like war, just as he proved to be a capable strategist as pope at war against Frederick II and in his dealings with Mongols. In his commentary, he treated war and licit violence in depth, in a section of the Decretals that considered whether ecclesiastics could repossess—by force if necessary—property occupied illegitimately.Footnote ²⁰ Rather than focus on the just intention, to which the Decretists often referred, or the moral guilt of the enemy, Innocent laid emphasis on the question of proper authority for war, for which he created a detailed hierarchy. At the highest level of justifed violence, he asserted that a full public war could be licitly declared only by a prince who did not have a superior (princeps non superiorem habet).Footnote ²¹ This was a notable contribution, as the Decretists had usually been less clear about which public, secular authorities had the capacity to wage wars.Footnote ²²

The significance of Innocent's formulation can be gauged from contemporary papal law, and particularly the bull Per venerabilem, promulgated in 1202 by Pope Innocent III. Among other things, the bull observed briefly that the king of France recognized no superior authority in temporal affairs.Footnote ²³ As has been well observed, some jurists, and often those from the monarchies of France, Sicily, Spain, and England, in the course of the thirteenth century declared that their kings recognized no secular superior and were sovereigns in their own territory.Footnote ²⁴ To make these arguments, the jurists asserted that European kings could and did possess in their own territory the same rights that the emperor possessed in his (rex in regno suo est princeps), which issued in a full power to order their internal and external secular affairs. These were important developments, as according to a fiction that perpetuated the unity of the classical Roman Empire, political entities in Europe were often argued in law to have a de jure superior in the medieval Roman emperor, an elected German prince. An assertion of freedom from any higher jurisdiction (superiorem non habet) expressed the independence of some nations from the empire, at least de facto.Footnote ²⁵ Certainly, Innocent IV appeared to use this formula to indicate that some kings were sovereign, and possessed a power to wage war on their own authority.Footnote ²⁶

Innocent's war waged by a prince who had no superior roughly corresponded to the public war described in Roman law as declared by the emperor, and carried with it some rights of Roman war. In these wars, now waged also by other sovereigns, acquisition of territory was licit, although the enslavement of captives was not generally practiced in wars within Christian Europe.Footnote ²⁷ For those wars in which captives could be enslaved—those fought beyond Europe and (in theory) fought by the emperor against his own rebellious subjects—there was a right of postliminium, whereby captives lost their civil rights and saw them restored when they were released or escaped to safety.Footnote ²⁸ There was little sense in which judgments concerning the justice of these public wars could be obtained from other temporal powers without the consent of the contending parties.Footnote ²⁹

The important legal and moral limitation on secular authority was the intercessory power of the papacy in temporal affairs. At the far end was the claim, made by some canonists and controversialists, and particularly in the thirteenth century, that the papacy had a supreme secular jurisdiction over Christendom; however, Roman lawyers were not generally attracted to this view.Footnote ³⁰ The papacy did, more successfully, assert a right to judge broken peaces and truces among Christians, as well as a right to intervene in secular affairs, on account of sin (ratione peccati).Footnote ³¹ The church had also claimed, from the tenth century, a leading role in peacemaking efforts, in the Peace and Truce of God movements. The activity of the papacy in hearing appeals and arbitrating disputes was not insignificant, particularly in the thirteenth century, but it faced real limitations in ending disputes between the leading monarchies.Footnote ³² In describing the right of independent powers to wage war, Innocent was not spurning the peacemaking role of the papacy, but rather was realistic about the legal effects that flowed from wars, particularly those between monarchs.

The more limited kinds of sanctioned public violence in Innocent's account reflected a broad scope of thought. These licit uses of public force can be fitted into four categories: limited wars on superior authority, punitive restraint of rebellious subjects, immediate self-defense, and reprisals. War on superior authority was generally intended to restrict petty feudal wars by requiring subordinates to appeal to their jurisdictional superiors for permission to wage war for the sake of recuperation, and reflected the customs of feudal society.Footnote ³³ The restraint of rebellious subjects Innocent termed an “exercise of jurisdiction,” by which anyone with territorial jurisdiction (in Innocent's example, a prelate) could pursue rebellious or lawless subjects and all those who helped them.Footnote ³⁴ There was also self-defense against immediate (incontinenti) violence to person or property, which was available to all without the authority of a superior. Innocent wrote that this was not properly termed a “war,” and did not carry with it the rights of war.Footnote ³⁵ Unlike some earlier canonists, Innocent was thus able to separate immediate defensive actions from public wars.

It was Innocent's reference to reprisals, however, that drew attention to the legal issue underlying the power of independent authorities to wage war. Under the procedure for reprisals, an individual from one jurisdiction who had suffered a legal injury could seek justice from the authority who had jurisdiction over the offending party.Footnote ³⁶ If justice was denied, a judge from the injured party's own jurisdiction could grant a license to recover damages from anyone of the foreign jurisdiction.Footnote ³⁷ Although reprisals were often a nonviolent remedy for aggrieved merchants, Innocent and other jurists included them as a species of war. Importantly, Innocent added that if there was no judge before whom the injured party could obtain justice, the party had the power to recuperate what he had lost on his own authority.Footnote ³⁸ It was this last point that Roman jurists would also take up in outlining a clearer juridical foundation for war among sovereigns. For some civilians, the lack of a judge would result in a right to judge one's own causes and wage war when (the offended party judged it) necessary based on prior injuries. Innocent's complex and careful treatment undoubtedly aimed to limit war, particularly among feudal nobles; however, his acceptance of secular sovereignty in Europe pointed to his understanding of political reality.Footnote ³⁹

II. Roman Law

Unlike canon law, Roman law, as it was recovered by medieval Europe in the eleventh century, and which became a foundation of legal training in continental schools for centuries, featured no theory to justify war. This fully recovered body of law, the Corpus juris civilis of Justinian, pertained to Roman citizens, and did not greatly concern itself with relations between nations.Footnote ⁴⁰ Moreover, for medieval Roman lawyers in particular, the Roman emperor was often accepted to have valid claims as the de jure secular authority over Europe, if not beyond. Wars of subordinate European authorities without the permission of the emperor typically seemed illicit to civilian jurists until the later thirteenth and fourteenth centuries.Footnote ⁴¹ On the other hand, the Corpus juris civilis offered some stimulus to discussion, by accepting war as a natural phenomenon. A noted passage in Justinian's Digest, D.1.1.5, stated that war developed under the law of nations, along with distinct peoples or tribes, the first governments, private property, and commercial relations.Footnote ⁴² The law of nations (jus gentium) was generally identified by medieval civilians as “secondary” natural law, or that part of natural law that pertained to humans alone, by virtue of their capacity for reason.Footnote ⁴³ As a result, war appeared as a natural and permanent custom, which under the right conditions was consonant with, or even required by, reason.Footnote ⁴⁴ This also harmonized with canon law, but unlike war in most canon law, the Roman law in Justinian's collection lacked a notion of war as punishment for sin or as guided by divine providence.Footnote ⁴⁵

Medieval civilians took this limited Roman material and slowly developed definitions of legally acceptable or licit war, based on a mixture of the rights of the Roman emperor and on principles drawn from Roman private law, which could be applied to independent polities in Europe. Franciscus Accursius (c. 1182–1263), author of the standard gloss on Roman law, described two kinds of licit war. The first were the wars of the Roman emperor, which appeared licit simply by the fact that he declared them.Footnote ⁴⁶ The second were wars fought to repulse injuries, which Accursius justifed by observing that a right of defense was available to all, according to natural law and the law of nations.Footnote ⁴⁷ Elsewhere in his gloss, the jurist admitted that there were free peoples and sovereigns who were not subject to the emperor, and suggested that fighting for one's country (patria) might be a duty.Footnote ⁴⁸ Although Accursius likely had the rising European monarchies in mind, he did not clearly identify the sovereigns to which this applied. In fact, he was more exercised by his contemporary Italy, in which he generally held that cities were not legitimate combatants (hostes) when they fought against each other, as they had a common superior in the emperor.Footnote ⁴⁹ The view cast doubt on the power of the Italian cities to engage in anything except immediate self-defense.

Although there was limited material in Roman law that directly addressed war, there were texts on personal self-defense and the recovery of despoiled property which contributed to juristic thought on the subject. Roman law held that “all laws and rights” allowed the use of defensive force against force, and medieval commentators developed two basic standards for defense, based on Roman texts.Footnote ⁵⁰ The first required that violence be repulsed immediately (incontinenti), whereas the second demanded that no more than a “moderate” amount of blameless violence be used in defense.Footnote ⁵¹ These standards were often interpreted broadly by medieval civilians. The criterion of moderation included, according to many medieval jurists, a right to strike first in case of a threat of violence, as it was reasoned that the initial attack could be deadly.Footnote ⁵² Granting a strong right of defense to individuals is not surprising in a period in which armed violence was reasonably frequent, but it is the later application of this theory to relations between nations that is significant for questions of war. This same medieval “pre-emptive” strike in Roman law, valid among individuals, was later cited in the sixteenth century by the civilian jurist Alberico Gentili (1552–1608), to help justify pre-emptive strikes between nations.Footnote ⁵³ Gentili expanded the notion to include war to prevent threats that were not immediate but only probable, or merely possible, and this more fully “humanist” account of justified war was supported by reference to classical historians.Footnote ⁵⁴ The first stated basis of the argument, however, was medieval Roman law and the opinions of civilian jurists, just as Thucydides was utilized to add a further dimension to the view.

The timing of defensive violence in medieval law was likewise important. In the Corpus juris civilis, anyone unlawfully dispossessed of property was to seek a judicial interdict to have the despoiled possessions restored.Footnote ⁵⁵ The interdict was open to anyone ejected from property by force, not only the just possessor. Such was the importance of judicial intervention, and the dim view taken in this case of self-help, in the classical sources. However, the medieval interpretation of self-help was again more generous. The French civilian Jacobus de Ravanis (or Jacques de Revigny, d. 1296), for example, held that someone ejected from his rightful property could wait and gather his friends for over a year, without judicial intervention, before returning to eject the unjust possessor by force.Footnote ⁵⁶ The standard for this criterion of immediacy, necessary for justified defense, was that the victim had not turned his mind to other affairs, which could be extended quite far in time. Certainly the standards of moderation and immediacy could be and were interpreted to support expansive rights of licit, extrajudicial force in defense of person and property. Jurists responded to contemporary social conditions in creating these rights, but had to balance their opinions against the possibility of licensing private vengeance.

Medieval jurists were aware of the issue of self-help, and sought to accommodate it within a legal framework in some cases. They had to contend, however, with Roman law texts that disallowed it. A passage in Justinian's Code (C.1.9.14) expressly held that one could not take vengeance for injuries oneself, and another, C.3.5.1, held that individuals could not be judges in their own (legal) causes or decide law for themselves (ne quis in sua causa iudicet vel sibi ius dicat).Footnote ⁵⁷ However, medieval civilians, from an early period, also considered the situation in which there was no judge to decide a dispute or settle the law. This was the same question that would arise for jurists when treating disputes—over rights, or any range of alleged injuries— between secular authorities who claimed jurisdiction over a given territory and independence from higher authority. Discussions on the topic developed by the twelfth century, when a right of punishment was contemplated for individuals in the absence of a judge. The early civilian, Placentinus (d. 1192), denied that one could have a right to punish others for alleged transgressions, even if a judge to adjudicate the matter was lacking.Footnote ⁵⁸ The influential Azo of Bologna (c. 1150–1230) considered another possibility more favorably, holding that when the judgment of a magistrate could not be had, the recuperation of what was rightful—although not punishment—could be licit on one's own authority.Footnote ⁵⁹

Jurists who contemplated licit self-help in the absence of a magistrate, eventually brought their insights to bear on the question of war. In the generation after Accursius, Jacobus de Ravanis enumerated four kinds of licit war, two of which echoed the great glossator.Footnote ⁶⁰ Jacobus named the wars waged in strict self-defense against force, and those waged by the Roman people or emperor, as legitimate.Footnote ⁶¹ The following two were novel, however. The first was drawn from a text of Justinian, which offered an exception to the Roman prohibition on punishing offenders without judicial recourse.Footnote ⁶² The passage granted any citizen a license to immediately apprehend and punish grievous offenders against public order, which included individuals who devastated fields at night or ambushed travelers on roads. The second was the case in which a creditor seized his fleeing debtor and took what was owed to him.Footnote ⁶³ Both were examples from private law, and seemed to rely for justification on immediate, grievous, and potentially unpunishable harm, but Jacobus cited these as examples of licit war and as analogies that could legitimize judgment and punishment in the absence of a judge.

Jacobus willingly referred his comments to his contemporary political context, applying his interpretation of private law to relations between polities. He noted that political adversaries might formally be part of the Roman Empire, but that when judgments from the emperor were not available, the adversaries could judge their own causes and wage war.Footnote ⁶⁴ The same applied, Jacobus observed, to polities that recognized no superior. While monarchs in England or France might assert their complete independence from the empire, it was particularly in Italy— where again the emperor's formal overlordship was usually accepted—that a lack of the copia superioris, or access to the judgment of the rightful superior, could be used to signify in law that the emperor was absent or impotent as a judicial authority. For Jacobus and subsequent discussion in Italy, the absence of the copia superioris was a recurrent feature in comments that cities could exercise a right to judge their own causes and wage war.Footnote ⁶⁵ The practical failure of the emperor's jurisdiction, however rightful, would likewise become a basis for asserting the independence and effective sovereignty of the northern Italian cities in the fourteenth century.

The Italian civilian Cinus de Pistorio (Cino da Pistoia, c.1270–1336/7) followed Jacobus in his analysis of licit war, although somewhat more conservatively.Footnote ⁶⁶ Cinus asked whether political authorities subordinate to the emperor could wage war against one another when the seat of the empire was vacant, as in that case, recourse to the judgment of the superior was unavailable.Footnote ⁶⁷ As a northern Italian himself, Cinus's question had reference to the Italian cities, and he held that defensive wars could be taken up when the empire was vacant.Footnote ⁶⁸ Cinus's younger contemporary, Albericus de Rosate (c.1290–1360), went further on the issue, but likewise did not ask whether the emperor's judgments might be regularly, or permanently, unavailable. Albericus considered whether, as “canonists said,” the church succeeded to the place of the emperor when the seat of the empire was vacant. He denied the possibility, arguing that the empire and church were independent of each other and could not succeed to each other.Footnote ⁶⁹ As a consequence, with the empire vacant, “arms were able to be taken up without [imperial] license.”Footnote ⁷⁰ Like Jacobus, Albericus noted that it could be licit to pass judgment or give law to oneself (sibi ipsi dicere ius) and to punish transgressors.Footnote ⁷¹ It was again the de facto absence of a rightful jurisdictional superior, or his inability to pass effective judgment, that led to a right of self-judgment.

A student of Cinus, Bartolus de Saxoferrato (1313/14–1357), made perhaps the most important contribution to the question in medieval Roman law. One of the outstanding jurists of the Middle Ages, Bartolus is noted in medieval political thought as the first to articulate a theory of sovereignty for the Italian cities. As Cecil Woolf described in his classic study, the cities' non-recognition of the emperor as a superior (non recognoscens superiorem), was at the heart of Bartolus's argument that the cities were independent and effectively sovereign.Footnote ⁷² Beyond a mere assertion of independence from the empire (accomplished effectively by usurping imperial rights and jurisdiction in their territories), the cities might exercise the rights of sovereignty by imperial concession, or by custom or prescription.Footnote ⁷³ As a result of their independence, Bartolus argued, some cities could exercise sovereignty within their territory, based on an analogy to the emperor's power over his own territory: a city could be an emperor unto itself (civitas sibi princeps).Footnote ⁷⁴ In reality, cities such as Florence or Venice had been sovereign for a long time, and their power could be seen (at least within city walls) in the control they exercised over their own secular affairs, including control over fiscal matters, the power to judge and punish secular cases, and exclusive power to make secular law.Footnote ⁷⁵ Another attribute was the right of the cities to wage war on their own authority, and Bartolus made comments on war that were inseparable from his theory of sovereignty, and partly underpinned it.

Bartolus argued for the cities' non-recognition of the emperor, but also observed the changed conditions in medieval Italy. He discussed the contemporary state of affairs at the beginning of his Treatise on Reprisals (Tractatus represaliarum), a work that gives a detailed procedural framework for reprisals and seeks to bring that quasi-judicial practice within the learned legal tradition.Footnote ⁷⁶ Like Jacobus, Bartolus cited the inability of the emperor to act effectively as the highest superior of the Italian cities, which left the cities to settle disputes among themselves. This was the other side of the argument on non recognoscens superiorem: while the cities in some cases grasped independence through non-recognition, they also had it thrust upon them by the inability of the emperor to effectively exercise jurisdiction. At the opening of the Treatise on Reprisals, Bartolus noted that in the time of the ancient Roman Empire, the emperor ruled effectively and no cause arose for dispute, reprisals, or war between the Italian cities.Footnote ⁷⁷ The contemporary situation, by contrast, was one in which the Roman Empire was helpless, and temporal authorities did not recognize it de facto. As a result, there was no recourse to a superior in disputes.Footnote ⁷⁸ Although Bartolus was discussing reprisals, the same conditions held for war; and although formally, the injured side was to first petition the other side for redress, the power to judge when retaliatory action or war was necessary rested finally with the injured party.Footnote ⁷⁹

Bartolus also gave further attention to the natural right of self-defense. In the Treatise, he affirmed that bodily protection was licit, according to the law of nations (or secondary natural law), and used medieval corporation theory to draw an analogy between an individual's right of defense and a collective right of defense that could be extended to political bodies. It was a point that was assumed earlier, in Accursius, and was not apparently questioned in medieval Roman law. However, Bartolus made the analogy clearer:

The comment alluded to a city as a mixed body (corpus mixtum), referring not only to its composition from a number of individuals but also to its corporate nature. Self-defense was permissible for the corporate polity qua whole or, as Bartolus noted, on behalf of an individual. Just as the individual could bear legal rights and duties, so too could the political body, according to a medieval legal theory by which the collective or corporate body was accepted as a collegium or universitas, and could be represented as a persona ficta, or single juridical person.Footnote ⁸¹ The right of self-defense could thus be applied through a familiar juridical concept to independent polities, including cities; and medieval corporation theory in general helped jurists to apply rights and principles drawn from private law to political bodies or “public” persons, and to disputes among them. It was a practice that became common in early modern “international” law and has continued (with and without theoretical justification) into modern international law.Footnote ⁸²

Like any medieval jurist, Bartolus considered self-defense to be a natural right, and it was a right that could not easily be denied to political entities. This was in contrast to many canonists, particularly the Decretists, who, as noted, did assume that the unjust (and guilty) side in war defended itself unjustly against just punishment.Footnote ⁸³ For Bartolus, independent polities possessed a strong right of self-defense and judged the justice of their wars, a view that is some testament to the growing power of independent polities in Europe, and the often more frank recognition in Roman law that war related to a question of jurisdiction. As something of a further step, Bartolus's right of defense, under which one could wage war (even “against all”) for self-protection and the protection of goods, vaguely calls to mind Hobbes's “warre of every man against every man” in his well-known depiction of a state of nature.Footnote ⁸⁴ Although apparently a distant comparison, there is at least some reason, which will be discussed, why Hobbes's state of nature might be considered not only from a legal perspective, but also in the context of the tradition on judging one's own cause.

Civilians following Bartolus typically allowed the independent Italian cities a right to wage war. In some cases, jurists explicitly reduced the criteria for licit war to proper authority, after considering the difficulty of adjudicating the just cause; although without dismissing the concept of a just cause. One of Bartolus's students, Angelus de Ubaldis (c.1327–1407), addressed the issue in a quaestio in which he asked whether two Italian cities had a right to wage war against each other.Footnote ⁸⁵ Angelus found that the cities, Verona and Padua, exercised sovereign rights in their territories and could go to war. His treatment was not without subtlety, as both cities were said to recognize the emperor, but because they held imperial vicariates by concession, each possessed merum et mixtum imperium in their own territories, which equated to sovereignty.Footnote ⁸⁶ There was, therefore, no one to judge the dispute in civil law, and Angelus admitted that determining the just side was doubtful.Footnote ⁸⁷ Each city could licitly judge its own cause, defend its rights, and also take spoils in war.Footnote ⁸⁸ Angelus was, perhaps, the first civilian to point to the difficulty of discerning the just side in war. This early development of the concept of bilateral justice in civilian analysis largely depended on Bartolus and the recognition of the lack of an effective tribunal among the cities, although Angelus used the concept of imperial concession to skirt the problem of the emperor's weakness as a judge.Footnote ⁸⁹

In the generation after Angelus, two civilians who made contributions to legal discussions on the justification of war were Raphael Fulgosius (1367–1427) and Paulus de Castro (d. 1441). Both furnished theories of war that were sensitive to the Italian context in which they worked, and both built on earlier thought, discussing the problem of war in relation to a lack of common judicial authority. Like Jacobus, Bartolus or Angelus, they appeared to move away from the just war tradition, which had often raised the question of moral intention as well as just cause and authority. Fulgosius treated the equality of adversaries in the absence of common superior authority, although he arrived finally at a traditional solution, in line with some views in canon law. Paulus, for his part, articulated a newly permissive theory of justified war that was rooted in the medieval tradition, but also reached beyond it.

Fulgosius addressed the problem of discerning the just side in war in his commentary on the Digest at D.1.1.5. He initially observed that the just side was uncertain among independent authorities in secular disputes, when no judge served as a common superior who could decide the case according to civil law. As a result, “by the best reasoning, the people established that war would be the judge of the thing.”Footnote ⁹⁰ It can be noted that Fulgosius understood each party to war as a litigant. The sides judged the justice of their own causes, but they judged, as it were, as petitioners, whereas war judged the matter itself. Fulgosius cited lines from Lucan's Pharsalia in support, and then made reference to Northern Africa, which had been captured by the Vandals and later recaptured by Justinian, ostensibly to show that legal effects flowed from just or unjust wars.Footnote ⁹¹ He held that proper authority was the essential criterion for licit war, and that proper authority depended upon the lack of a superior. The kings of France, Aragon, and Castile, and any free people (including the independent cities of Italy) were given as examples of polities that asserted independence and sovereignty, and could wage war on their own authority.Footnote ⁹²

Fulgosius's opinion and the classical references he included were unusual, but his final solution returned to a position influential in canon law and beyond, which would continue to carry important weight. After arguing that war itself was a judge, he wrote that the pope was the common superior in Europe and that full Roman war was licit only between Christians and barbarians (those outside Europe), not among Christians.Footnote ⁹³ Strict self-defense against force was always licit, but Fulgosius saw a strong role for the pope in mediating and adjudicating European disputes, and bringing two or more sides to peaceful resolution.

III. Paulus de Castro

Paulus de Castro recorded perhaps the most permissive account of war among jurists in the period, and also discussed the question of judging one's own cause in a way that more clearly foreshadowed the states of nature of Thomas Hobbes (1588–1679) and John Locke (1632–1704). Writing on the problem of legitimate authority, Paulus repeated the point that an individual, having been wronged, could wage war against another when recourse to a superior was unavailable. Lacking the possibility of recourse to a superior, Paulus assured that it was licit for the individual to pass judgment himself (quilibet sibi ipsi poterat ius dicere), but he was more explicit than Bartolus in suggesting a state in which individuals could act as their own judges. As he wrote in his Digest commentary: “For also before there were magistrates, anyone was able to pass judgment himself by the law of nations; after the creation of magistrates, however, it was prohibited for anyone [to judge] on his own behalf…if therefore a magistrate is lacking, we remain in the disposition of the law of nations.”Footnote ⁹⁴

The description reinforced Bartolus and others on the right to judge one's own causes or decide law for oneself, but was striking for imagining a general condition of rightful self-help among individuals. The issue seemed to have more than a momentary interest for Paulus, because in a consilium, or legal opinion on a particular case, he again described the conditions under which it was licit to pass judgment on one's own behalf. There he returned to the idea of a state lacking civil magistrates, and identified a right of war. “Before laws were made, when there was no judicial order, which then was unknown, anyone pursued his own right (jus). But [afterward, there were judgments] either by a royal hand, if there was recourse to a king…or if there was no recourse, war was taken up on one's own authority (auctoritate propria). Indeed that seemed licit by all divine law, namely natural law and the law of nations.”Footnote ⁹⁵

With the enactment of civil laws and magistrates to protect the laws, public discipline was established. Prior to civil society, or when magistrates were lacking, Paulus indicated that each individual was effectively sovereign: [It is] otherwise if access to a magistrate is lacking, because it is not enough that laws (jura) were created, where there is no one to safeguard them…[in that case] we return to our primeval rights (jura), by which it is licit for us by every law (jure) to pursue our own right (jus nostrum), on our own authority (propria auctoritate).Footnote ⁹⁶

Translating the different senses of jus in the passage—which can equally mean “law” or “right”—is difficult, but Paulus clearly held that individuals possessed a right or licit power, in the absence of effective authority, to pursue justice for their property and person.Footnote ⁹⁷ Lacking magistrates, individuals were still able to observe those practices and institutions that were rightful under the law of nations (jus gentium), taken as the natural law of humankind, and which, for medieval jurists, was a basis for more local laws.Footnote ⁹⁸ According to Roman law, not only war, but liberty and private property, as well as self-defense, obligations, contracts, commerce, and slavery all arose under the law of nations.Footnote ⁹⁹ Jurists such as Paulus in the jus commune tradition would hold that the law of nations was valid in the absence of local law, and Paulus's comments in his consilium were prefaced to a dispute over land.Footnote ¹⁰⁰ How property was first acquired under the law of nations cannot be examined here, although medieval thinkers did theorize the first acquisition of property, and opinion (then as now) varied.Footnote ¹⁰¹

A case in which all individuals had a license to defend and pursue justice for their property and person (and to enforce things such as contracts) against all others, on their own authority, would seem to raise a perennial threat of war. In this connection, there was a greater potential for the development of a Hobbesian state of nature, in which each individual would be a sovereign and judge on one's own behalf, and to which Paulus's conception may bear some brief comparison. As Hobbes wrote in Leviathan: “in the condition of Nature, where every man is Judge, there is no place for Accusation.”Footnote ¹⁰² In his Elements of Law, he brought up the same problem: “In the state of nature, where every man is his own judge…arise quarrels, and breach of peace; it was necessary there should be a common measure of all things that might fall in controversy.”Footnote ¹⁰³ For Hobbes, in the state of nature, each individual has a right to everything, as far as the individual thinks it promotes survival. Because there is no authority, and no assurance of what is sufficient for self-preservation—and humans generally act according to fear and self-interest, while exhibiting qualities such as covetousness or vainglory—no one can be secure and the state of nature is a state of perpetual war.Footnote ¹⁰⁴

From a legal perspective, it might be suggested that Hobbesian individuals tend to be bad judges of their own causes in a state of nature. Hobbes certainly argued that humans are swayed by their passions and opinions, which are for him self-regarding; but where common judgment and security are absent, reason leads them to preserve themselves by whatever means seem necessary, which issues in an unlimited “right” for all.Footnote ¹⁰⁵ For Hobbes, in the state of nature there was no injustice. Hobbes's solution to the state of nature supposed that individuals would covenant to set up a sovereign, which individual or assembly would maintain the structure of a civil society. Among other things, the sovereign create and uphold civil laws, what Hobbes identified as natural laws or laws of nature, and would judge disputes and enforce decisions. He would also do so justly, although there was nothing to counter the sovereign.Footnote ¹⁰⁶

Hobbes had described a very minimal law which individuals acted on in the state of nature. The primary law of nature directed humans to seek peace for the sake of self-preservation, but as the primary right in a state of nature, humans could again preserve themselves by all means. As a second law of nature, individuals were willing to enter into contracts and voluntarily limit their right to all things if others also agreed, although without a common superior authority to enforce them, those agreements were too fragile to be sustained, and were in fact invalid.Footnote ¹⁰⁷ Hobbes supplied a further list of laws of nature, drawn partly from juridical sources, but these could not be acted on with prudence in a state of nature, since the law or rational precept of self-preservation in such adverse conditions trumped them.Footnote ¹⁰⁸ For Paulus and any jurist in the jus commune tradition, on the other hand, somewhat more substantial legal relations existed between individuals, as well as nations, in the absence of a common superior. These were based on natural law and the law of nations, and a natural justice that all humans were able to recognize and follow by reason.

The state lacking superior authority that Paulus described, if somewhat extrapolated, appears closer to the state of nature found in Locke, who saw the potential for dispute and war, but likewise thought that individuals could follow a somewhat fuller idea of justice in the absence of government.Footnote ¹⁰⁹ Similar to Paulus and views based on the law of nations, Locke asserted the existence of private property and a natural right to defend it, as well as life (including health) and liberty in a state of nature. He then offered to every individual in that state a striking, universal right to punish any transgressors against those limited rights.Footnote ¹¹⁰ From this also came a right to enslave anyone who seriously violated those natural rights, which was not unlike how slavery arose under the Roman law of nations.Footnote ¹¹¹ Locke explicitly equated this right of punishment with a right of individuals “to be judges in their own cases,” which included the right to seek reparations for injuries committed against an individual's own life, liberty, or property.Footnote ¹¹²

Locke's state of nature, and his theory of government, depended upon the notion that what was just in respect to the rights of life, liberty, and property could be recognized by individuals, by means of reason and in accordance with natural equity. Against the Hobbesian objection that, as judges in the state of nature, humans were partial to themselves, and that confusion and war would result, Locke admitted that civil authority was more convenient and preferable, but observed that it was susceptible to the same partial and self-regarding actors (i.e., tyrannical government) as would exist in a state of nature.Footnote ¹¹³ The power to punish grave violations of natural law in regard to life, liberty, and property remained with the people, taken corporately after the formation of civil authority; this power was rooted in the people's capability to justly judge violations, and led to a right to remove tyrannical governments.Footnote ¹¹⁴ For Locke, the state of nature and war were distinct: war was a condition of enmity, based on declaration or obvious intention to cause death, whereas the state of nature simply lacked a common superior judge between individuals, as was the case between independent governments.Footnote ¹¹⁵

In Paulus's account of a state of nature, it was unclear (and unlikely) that there was such a generalized right of punishment against any transgressor, although rights in property, liberty, and life could be justly discerned and defended by individuals who possessed them. Following the common medieval assumption that Locke also relied on, Paulus would agree that humans were able to understand what was rightful according to natural law and what was owed to others by reason, and could follow this justice and equity at least to some extent in a state of nature.Footnote ¹¹⁶ The situation would apply equally to individuals and to political authorities lacking a superior. On the other hand, Paulus did not consider that a natural (and quite expansive) right of defense among independent political authorities might be limited or invalidated in some cases, which posed challenges for an idea of enduring peace or justice, especially given the common right to judge and pursue one's own rights by war. The problem of the state of nature, at least—for a theorist such as Paulus in the medieval tradition or Hobbes and Locke in the early modern period—related not only to defining spheres of liberty for the individual, but to discerning and following justice in respect to practices and institutions that licitly existed in that state. The questions raised had as much to do with law as they did with rights.

The medieval juridical theory on the right to judge one's own causes in the absence of superior authority was apparently known to Hobbes and Locke, and served as a basic legal foundation of their analyses of a state of nature. Of course, neither Hobbes nor Locke cited legal sources from the medieval jus commune directly in discussing their states of nature. Their conceptions are also much richer than that of Paulus or other juristic discussions, and can be fully understood only in the context of their own period. But Hobbes and Locke knew and relied on legal sources, and Hobbes in particular may have been aware of legal questions on war from a near-contemporary like Alberico Gentili, who taught Roman law at Oxford when Hobbes was a student, or certainly from his own knowledge of law.Footnote ¹¹⁷ As Gentili wrote, indicating the most basic issue: “there cannot be judicial processes between sovereigns unless they themselves consent, since they acknowledge no judge or superior.”Footnote ¹¹⁸ Both Hobbes and Locke responded to the question of justice in the absence of a common superior; Locke interpreted the right to judge one's own causes, when lacking the copia superioris, in ways consonant with the medieval tradition, while Hobbes deeply critiqued that tradition.

Paulus, incidentally, articulated another theory of justified war, and this second theory stemmed directly from classical sources and a classical view of relations between nations. Whereas his first theory was a continuation of issues raised within the jus commune, the second theory likely relied on Aristotle and Cicero. In his Digest commentary, Paulus gave as causes for just war the recovery of goods lost (taken by stealth or open force) which could not be recovered otherwise, and the failure of a ruler to do justice, which went back to Augustine and Roman legal sources,Footnote ¹¹⁹ but the jurist added a third kind of just war, the war for the sake of ruling others well. This would easily result in permanent conquest, and he seemed to accept that these wars could be fought for glory:

Here Paulus offered a vision of war that departed from Christian just war theory (and part of classical legal tradition) but was not inconsistent with other classical views. Cicero had also held that wars could be fought for glory as a secondary aim, but it was Aristotle who argued in the Politics that empire for the sake of ruling others well was acceptable and praiseworthy for those of outstanding virtue, over people who were inferior.Footnote ¹²¹ Nor was Paulus's theory only directed at infidels, barbarians, or other “inferior” peoples outside the borders of Europe. The “free peoples” able to wage these wars included the independent Italian cities, and European monarchies against each other.Footnote ¹²² The war for ruling others well was still virtuous and rational, although it operated according to a classical standard of virtue. This last view of Paulus on wars, applicable within Europe, seems to represent the farthest point reached in Roman law before the late Renaissance or early modern period, from the traditional views on war in canon law.

IV. Concluding Remarks

Despite his last opinion, Paulus's theories of justified war fall generally within a medieval tradition. In large part, this was a medieval Roman law tradition, in which the right of sovereigns to judge their own causes, the shadow of Roman imperial rights, and an idea of pre-emptive defense, made for strong rights of war. Beneath these ideas was the Roman law of nations, understood as a limited set of practices and institutions considered natural and rational for human societies, and that accorded with the necessities of common human practice.Footnote ¹²³ The law of nations existed prior to and in the absence of local laws and customs, was not invalidated by them, and created very modest or minimal obligations between individuals or polities. It can be suggested that rights of war coming out of Roman law, based on an awareness of the problem of jurisdiction between sovereigns and featuring few laws between them, exerted a measure of influence on early modern accounts of morality that, as Tuck argued, featured strong rights of self-preservation and emphasized individual self-interest.Footnote ¹²⁴ At the same time, however, Roman private law provided the largest quarry of legal principles for early modern treatises on laws of war, allowing for more detailed regulations, which could be labeled as a much expanded law of nations and early international law.Footnote ¹²⁵

The argument by at least one civilian jurist that wars might be justified for the sake of ruling others well, and for the sake of glory, is outside of the tradition of war in medieval legal thought, and appears to share an element of a “humanist” approach on Tuck's classification. These views are believed again to validate robust rights of war based on classical sources, and to emphasize the secular, civilizational superiority of ancient Greece and Rome (and early modern Europe) over and against inferior barbarians and outsiders. As importantly, Tuck's account identifies classical skepticism and Stoicism as key early modern foundations for a minimal, universal set of norms, reducing largely to self-interest, which were applicable between individuals in a state of nature, as well as between nations, and even within civil society.Footnote ¹²⁶ Paulus's “humanist” contribution was more modest: he likely relied on familiar texts from Cicero and Aristotle's Politics, although his use of them was unusual in law.

Paulus's theory of war for conquest, insofar as it has a humanist aspect, is probably best viewed in his own historical and political context, and perhaps as the jurist's acceptance of some of the territorial aims of the ambitious northern Italian city-states in which he worked.Footnote ¹²⁷ The governments of the competitive cities of early fifteenth century Italy were flattered by praise and even imperial rhetoric from urban humanists, following on their foreign interventions, bellicose expansionism, and pursuit of glory within the Italian peninsula.Footnote ¹²⁸ This is one part of the well-studied early Renaissance culture of “civic humanism,” which flourished during Paulus's career.Footnote ¹²⁹ However, humanism did not seem to influence Paulus or his legal thought unduly. For a truly “humanist” view on war, or at least the kind of realism found in Hobbes or earlier in Machiavelli, new assumptions about human nature and its capacity (or incapacity) to fulfill the dictates of natural law would be needed. Indeed, the character and status of natural law would have to be redefined in some cases. As Tuck argued, an engagement with classical history and classical moral theory could aid this shift. On the question of war, Paulus stood on the threshold of some of these Renaissance and early modern developments, but remained within an older and influential tradition.Footnote ¹³⁰

Taken together, Roman jurists in the late Middle Ages contributed new opinion on war, and their interpretation of licit war typically differed from the earlier canonistic tradition of just war. For civilians, given proper authority to wage war, it was in practical terms acceptable to do so unless, as one civilian later wrote, the cause for war was “manifestly” unjust.Footnote ¹³¹ The jurists' contributions arose from a society in which effective political authority was often local, but also tracked, to some extent, the rise of powerful, sovereign polities in Europe. With Paulus de Castro excepted, the goals of secular wars within Europe were generally the same across the medieval jus commune, and were to relate to defense, recuperation, or punishment of specific injuries to property, person, or other rights. Given the legal independence of sovereigns, forms of mediation and legal arbitration would have to play a role in resolving, deferring, or lessening the intensity and duration of conflicts,Footnote ¹³² but from a Roman perspective in particular, it was doubtful that a right of defense, or other rights without consent, could be limited or forfeited by sovereigns on account of alleged violations and injuries. By granting sovereigns robust rights of war, medieval civilians were attempting to respond to their own fractious, contemporary environment, much in the way that Gentili or Grotius, or indeed Hobbes or Locke, would do later.