 Bessarion’s opera omnia include writings prepared for audiences in both the Byzantine and the Roman courts, such as orations and pieces of poetry. Of particular interest are the orations he addressed to Italian rulers, in order to convince them to join a crusade against the Turks (the Orationes ad principes Italiae contra Turcos, 1470). The De errore Paschatis, devoted to calculating the proper date of Easter, was probably composed with the assistance of Regiomontanus (1436–1476) and reflects Bessarion’s early interest in astronomy, which he had cultivated since the time of his training under Cortasmenos and Pletho. Bessarion also left behind a rich corpus of letters which he had never edited for publication. In addition to being the patron of important translations, he also himself translated Greek works into Latin, including Saint Basil’s De nativitate Domini, Xenophon’s Memorabilia, and Demosthenes’ First Olinthiac. However, Bessarion’s most important works, both as an author and as a translator, are focused on theology and philosophy.