As he did successfully with pairs of volumes on Suetonius’ De grammaticis et rhetoribus and Macrobius’ Saturnalia, K. has produced an indispensable resource for those who wish to study Suetonius’ Caesares in the original. Scholars have relied on M. Ihm's redoubtable Teubner edition since its first appearance in 1907, but now K.’s edition will be the standard text for a long time to come.

The entire extant manuscript tradition of the Caesares stems from the re-emergence of Suetonius in the time of Charlemagne, and K., through his own study of the manuscripts, is able to build on the work of his nineteenth-century predecessors to clarify the descent of two branches from the archetype, labelled α and β, showing that the former were products of north-central France and the latter from the Norman territories of north France and southern England (OCT, pp. ix–x). Within the β manuscripts, to which editors since K. Roth have all paid little attention, K. illuminates the singular influence of William of Malmesbury, whose text (ζ in K.’s sigla) lies behind C and H and demonstrates how a distinguished scholar set about correcting the text he had received. Having studied ζ more thoroughly than Ihm, K. is now able to attribute to William 64 corrections and to show that such corrections, previously attributed to Renaissance or early modern scholars, were first made in the twelfth century (see Studies, pp. 287–90). From his discussion of the ‘contamination’ between the α and β branches K. produces a very helpful stemma (OCT, p. xl) that shows the chronological relationship of the individual manuscripts and the linkages amongst them.

From his painstaking full collation of eighteen manuscripts from the fourteenth and fifteenth centuries, K. offers 33 individualised sigla for the undifferentiated siglum of Ihm and L. Preud'homme and is able to conclude that the recentiores do not offer a new route back to the archetype. For readings from printed editions of Suetonius that were produced from 1470 K. provides revealing statistics for the 390 emendations that his edition incorporates: S. Iadertinus, F. Beroaldus, R. Stephanus, I. Casaubon, Roth and Ihm contribute significantly to the 207 made by earlier editors, while R. Bentley, L. Torrentius and J. Lipsius feature prominently among scholars whose views K. follows.

K. is singularly helpful to his readers in establishing the differences between his text and that of Ihm, his most authoritative predecessor and a cautious editor: appendix 5 of Studies lists all the differences. In relation to the 309 passages in this list, fourteen times K. prefers a reading from ζ (see Studies, p. 290), 189 times K. prints an emendation suggested by scholars since 1470 and provides sixteen new emendations of his own.

From these we can see something of what K.’s study has brought to the text, for example: at Aug. 40.3 K. proposes quasi for the manuscripts’ quam or Bentley's quod, on the basis that Suetonius uses it again in connection with promittere at Tib. 21.2. At Aug. 67.2, where Ihm printed crura ei fregit, K. excludes ei as an interlinear gloss on the basis of Suetonius’ usage of resumptive pronouns (arguing against J. Gronovius), which means that fregit can have its regular meaning. At Tib. 43 K. posits a lacuna between habitu and quae, indicating rightly that the various attempts to emend the manuscripts’ -que are inadequate. At Claud. 36.1, to Ihm's nihil tota via quam essetne sibi salvum imperium requires, K. adds an aliud immediately after the nihil, which produces a combination Suetonius uses seven other times in the Caesares and produces the right sense. On a similar line at Claud. 10.2 K. replaces the manuscripts’ adhuc with aliud to produce nihil quicquam aliud quam frementis perduxit, another Suetonian combination that enhances the sense. To the vexing introductory sentence of Suetonius’ rubric on Claudius’ public works (Claud. 20.1), by simply eliminating one of the two quams, K. produces not just sense but a statement by Suetonius that perfectly ties in with the content of the chapter that follows: opera magna potius {quam} necessaria quam multa perfecit. At Galb. 7.1 K. plausibly posits that etiam is a gloss of the et that follows it in α and produces the phrase et in parvulis that perfectly completes the sense of iustitiae cura.

Only one of K.’s own emendations seems questionable: at Tib. 40 K. inverts the two words that H. Polak adds to the text tanto mag <is mirantibus cunct> is quod urbe egrediens ne quis se interpellaret edixerat. While the sense K. provides is wholly appropriate, Polak's supplement reflects better Suetonius’ regular word order in combinations of cunctis with a present participle and where there are no intervening words (Iul. 82, Aug. 37, 58.2, Calig. 14.3, Claud. 21.1, Ner. 35.2, Vit. 4.1; cf. Vit. 15.2), i.e. the participle stands first.

While it would not be right to call K.’s a radical edition of Suetonius’ Caesares, he is considerably bolder than Ihm in admitting scholarly conjectures into his text, and in the vast majority of cases I found myself approving his decisions. A rare case, where K. might have gone further than Polak, is at Iul. 82: given that Suetonius supplies full praenomina throughout the section, why introduce just the abbreviation L. in the case of Lepidus? At Ner. 12.4 K.’s decision to stick with the manuscripts’ pretiosissimis margaritis adornatam Capitolio consecravit rather than to add in, as he suggests is worth considering in the apparatus, is a missed opportunity: if Capitolio is a locative, it is unique in Suetonius for places of dedication; if it is a dative after consecro, Suetonius employs that case for the deity to whom the dedication is made, not for a place. It seems that Casaubon was on the right track by suggesting Iovi Capitolino, but Suetonius regularly places the epithet before the noun – in this case Iovi might easily have been lost after Capitolino.

I found only one case of inconcinnity between the two books: on Iul. 53 at Studies, p. 75, K. says he prints appetisse dicat, but the OCT has appetisse scribat. Of significant typos, which are remarkably few for works with such complex setting, at Aug. 83 in the OCT segresti should be segestri; in Studies, p. 227 on Galba 8.1 ingresses should be ingressus and on p. 299 on Divus Titus 7.1 in both cases suspectus should be suspecta.

The two books are the fruit of immense labour by K. that display a remarkable feeling for Suetonius’ language. He has produced an excellent edition and exemplary explanations for the choices he has made. Even where scholars may disagree with K., they will have his clearly argued decisions to reckon with. Mrs Kaster's sufferings (see Studies, p. 267) may sub specie aeternitatis be outweighed by the benefits to generations of readers of Suetonius.