Basil Bessarion (1403?–1472) was a key political and cultural figure in mid-fifteenth century Europe. Born and raised an Orthodox Christian in what was left of the Byzantine Empire, he became a fervent supporter of the union of the Latin and Greek Churches in 1438, when he moved to Italy for the Council of Ferrara-Florence. Bessarion devoted his life to preserving Greek literature and championing military ventures that might restore the Byzantine Empire. One of his most important political achievements was to persuade the Venetian Senate to declare war on the Ottoman Empire in 1463, which led to the First Ottoman–Venetian War (1463–1479). Two months earlier Bessarion had written and circulated in both Greek and Latin the Encyclica ad Graecos, a theological, canonical, and political pamphlet calling for the union of all Christians against the Ottomans. My research aims to investigate the philosophical and rhetorical strategies employed by Bessarion in writing the Encyclica and its impact on the debate that preceded Venice’s declaration of war on the Ottomans.