Constantinople fell to the Ottoman Turks in 1453. After that triumph, the Ottomans continued expanding their control of the Balkans. In response, the papacy attempted to organize crusades against the Ottomans with limited success. Pope Pius II (r. 1458-1464) tried to combine a crusade with a letter intended to convert Sultan Mehmed II to Christianity. The letter probably never was delivered. Similarly, in 1466, George of Trebizond wrote two letters to the sultan, one dated to February and the other to October of that year. The first letter addressed Mehmed as emperor of the Romans, victorious by his virtues and divine permission. That would, according to the second letter, make him emperor of the whole world. George made no effort to refute Islam or persuade Mehmed to convert. Awareness of these letters caused Pope Paul II (r. 1464-1471) to consign George to the Castel Sant’ Angelo. Although he was released in 1467, George was the target of a refutation of his ideas by Rodrigo Sánchez Arévalo, his jailer, who was commissioned by Pope Paul to write it. (Rodrigo also had custody of members of the Roman Academy.)

Rodrigo was a canon lawyer who had been in the service of the king of Castile and then of the popes. His several writings included, as Mazzanti shows, statements about lay and ecclesiastical power. His stance favoring Pope Eugenius IV over the Council of Basel had endeared Rodrigo to pope and curia. Mazzanti does not mention that Nicholas of Cusa had addressed to him a letter interpreting away the division of pope and council in the light of “learned ignorance.” This known fact Mazzanti omits, as he does Cardinal Juan de Torquemada’s polemic defending the Roman Empire against Rodrigo’s political writings. Nonetheless, Mazzanti’s biographical sketch of Rodrigo Sánchez is brief but useful.

Rodrigo fulfilled this commission with his Liber de et infelicitate perfidi turchi ac spurcita et feditate gentis et secte. This tract can roughly be dated to the time when George was a prisoner. It consists of a brief prologue addressed to the pope and refutations of twenty “errors.” Each copy has a table noting the errors refuted in the twenty sections. The text survives in only two manuscripts. The copy in Vaticanus Latinus 971, fol. 6r-124v belonged to Cardinal Bessarion. That in Vaticanus Latinus 972, fol. 1r-102r belonged to Pope Paul, the dedicatee. Mazzanti carefully notes the differences between the two manuscripts, concluding that Vat. Lat. 971 is, overall, the better base for an edition. The edited text has two sets of annotations, one noting where Vat. Lat. 972 has different, occasionally better, readings. The second set of notes indicates the sources Rodrigo used, not just the Bible, theology and law, but some classical and translated Arabic sources.

The ideas Rodrigo attacks fall roughly into two categories. Errors I-XII concern the ability of the sultan to be an emperor and have a right to wide dominion. It also attacks the Turks and Islam. Mehmed is dismissed as possessed of vices and following an erring religion. All, sultan, people and faith, are dismissed as devotees of sexual pleasure not of sound morality. Mehmed is contrasted too with Christian rulers like Constantine. The Castilian canonist made use of the Donation of Constantine in the creation of this contrast. There is no sign that he knew of the arguments of Cusanus and Lorenzo Valla dismissing that text as false. Nor did conquest justify any claim to being an emperor of the Romans. Rodrigo’s text leans heavily to papalism, including the idea that a pope had to authorize translation of empire.

The other errors (XIII-XX) concern George’s perceived dismissal of the Catholic faith. This included arguing that the sins of the clergy made them unworthy to hold power. Because of their sins, rule could devolve to lay rulers. This, in turn, opened the way to rule of Christians by the Turks. Rodrigo’s answers upheld the idea that the sins of priests did not vitiate the effectiveness of their sacraments. Moreover, devolution of power even to Christian princes meant allowing power to fall from superiors to inferiors. In no way was rule to pass to a people lacking right belief and right living.

The Liber de et infelicitate perfidi turchi ac spurcita et feditate gentis et secte is not a notably original work. However, it illustrates ideas common in Rome during the 1460s. The Turks often were dismissed as infidels living filthy lives. Mehmed himself was dismissed in similar terms, and no concessions were made to Islam. (The limited value granted to the Qur’an by John of Segovia and Nicholas of Cusa finds no place here.) The Donation of Constantine still had a place in papalist polemic, and no challenge was admitted to the supremacy of the Roman pontiff.