In fifteenth-century Rome, Ethiopian pilgrims responded to the locals’ persistent questions with increasing bewilderment: “Our king is Zara Yaqob; why do you call him Prester John?” (Paul Freedman, Out of the East: Spices and the Medieval Imagination [2008], 198). The legend of Prester John—a Christian priest-king in the Far East who ruled a terrestrial paradise overflowing with gold, spices, and other treasures—dominated medieval European ideas of the world beyond the shores of the Mediterranean. Much of the curiosity resulted from a spurious letter from Prester John to the Byzantine emperor Manuel I Komnenos, which began circulating in Europe around 1165, describing the marvels and riches of his kingdom. While this was originally believed to be located in India (and connected to the evangelization of Saint Thomas), later authors placed it first in western Asia and then in eastern Africa; hence the curiosity about Ethiopia.

Scholars have debated the authenticity of the letter to Manuel and the existence (or otherwise) of its author—or at least the identification of this “rich Christian priest-king in the East” with any historical figure—for centuries. Most now agree that the letter was probably written in the milieu of the court of Frederick Barbarossa (1155–90) to support the principle of sacral kingship against contemporary papal claims to temporal power. Giardini's book takes a new perspective, however: while he addresses the political and ideological implications of the Prester John legend, his main focus is on how the Christian legend of Prester John intersects with the Jewish legend of the ten lost tribes of Israel. Supposedly, the ten lost tribes had been exiled east beyond the Sambatyon River by the Assyrians and would return to the land of Israel in the end days; the two legends, therefore, shared not only an interest in the marvels of the East and the earthly paradise, but also similar mystical and eschatological implications.

Giardini begins with a historical and philological review of the respective origins of the two legends (chapter 1), and analyzes how they came to be connected in the two traditions. He then studies (chapter 2) how the joined legends developed in the later twelfth and thirteenth centuries, especially in the context of growing Christian anti-Judaism (especially the condemnation of the Talmud in 1240). Chapter 3 focuses on the interweaving of the two legends in the Hebrew tradition, where the reports of numerous travelers claimed to have found the tribes or evidence thereof. Finally, Giardini provides a matched pair of chapters paralleling the “doctrinal and symbolic aspects” of each legend in its own tradition: Jewish (chapter 4) and Christian (chapter 5; quoted phrase from chapter titles, pages 159 and 223). The appearance along the way of Benjamin of Tudela, Alexander the Great, Gog and Magog, Joachim of Fiore, the Sefer Zerubbavel, and the Holy Grail give a sense of how far-reaching these legends were between the twelfth and sixteenth centuries, and how they seized the late medieval imagination—especially insofar as they connected predictions about the end of the world with information about the marvelous East, both topics about which contemporary Europeans were intensely curious.

The book is therefore written from a consciously comparative perspective, combining matters of politics with those of theology, geography and cosmography, and symbolism in the Christian and Jewish traditions; sometimes these traditions parallel each other but more often they intertwine. While Giardini's approach occasionally results in sections that appear disconnected from the main argument (the labeling of certain sections as “excursuses” seems to undervalue the material they contain), he generally succeeds in drawing together diverse threads that run in many different directions, demonstrating their underlying similarities, and laying out the historical circumstances that connected them.

Globalism—as in the global Middle Ages or global Renaissance—has recently received a great deal of attention as a subfield of medieval and early modern studies. Along with renewed interest in trade networks and travel narratives, the question of what late medieval Europeans knew or thought they knew about the world beyond Europe has proved especially thought provoking, especially with regard to how it affected the course of world events in the fifteenth and sixteenth centuries. Since Prester John dominated such ideas for centuries, Giardini's work joins a distinguished but newly vibrant line of research on the Prester John legend, with the added benefit of contextualizing the legend within a broader, conjoint Judeo-Christian intellectual tradition.