The adversaries of the title were Georg of Trebizond (1395–1472) and Basilios Bessarion (1403–1472). There is an ironic twist to their names. George of Trebizond derived his name from his ancestors, who originated in the Empire of Trebizond but he was born in Crete. His later antagonist Basilios Bessarion, however, was born in Trebizond.

At sometime unknown point, whilst he was still relatively young, George of Trebizond moved to Italy, where he learnt Latin and acted as amanuensis to the politician Francesco Barbaro (1390–1454) in Venice. A brilliant Aristotelian scholar he entered the entourage of Pope Nicholas V (1397–1455) a convinced Aristotelian.

Basilios Bessarion was educated in Constantinople then went in 1423 to study Plato under Georgius Gemistus (c.1355–c. 1452), known as Plethon, a highly influential revivalist and teacher of Neo-Platonism. He became an orthodox monk, advancing to abbot in 1436 and metropolitan of Nicaea in 1437. In 1439 he travelled with the Orthodox delegation to Italy to try to persuade the Catholic Church to join the Orthodox Church in a crusade against the Ottoman Turks. Bessarion’s political position led to him being heavily criticised in Byzantium and so he stayed in Italy where Pope Eugene IV (1383–1447) appointed him a cardinal of the Catholic Church. A convinced humanist he devoted his life to spreading support for humanism and to amassing a large private library, containing an extensive collection of Greek manuscripts. He presented his library to the Senate of Venice in 1468 and the 482 Greek manuscripts and 264 Latin manuscripts today still form the core of the St. Mark’s Biblioteca Marciana.

Initially Bessarion and George of Trebizond were friends and Bessarion did much to support his colleague. However in the early 1450s their friendship began to unravel. In that year George undertook a translation from Greek into Latin of Ptolemaeus’ Mathēmatikē Syntaxis or as it is better known the Almagest, as a replacement for Gerard of Cremona’s twelfth-century translation from Arabic. Bessarion lent him his best Greek manuscript for the purpose and suggested that he used Theon of Alexandria’s Commentary, as a guide. He duly produced his translation and an extensive commentary in nine months finishing in December 1451. His work was hurried, sloppy and strewn with errors and the Pope’s evaluator Jacopo di San Cassiano (ca.1400–ca.1454) judged the work deficient and the Pope, Nicholas V, rejected the dedication. Bessarion took issue with George’s treatment of Theon. The incident ruined George’s reputation and he was forced to flee from Rome.

The situation between the two Greek immigrants escalated when in 1458 George published a vicious attack on Plato in his Comparatio Aristotelis et Platonis, which historian James Hankins has described as “one of the most remarkable mixtures of learning and lunacy ever penned.” In this work he accused Plato of being a traitor to Athens, a besmircher of rhetoric, an advocate of paedophilia, and a pagan who lent aid and comfort to Greek Christians. Bessarion, a Platonist, could not let this stand and issued a powerful response, In calumnatorem Platonis, which was printed in 1469. The situation became even more heated when George offered to dedicate his Commentary on the Almagest to Mehmet II, the Ottoman Turk Sultan, who had conquered Constantinople and ended the Byzantine Empire. George entreated Mehmet to convert to Christianity, to conquer Rome and thus to unite Islam and Christianity under his sovereignty. Bessarion got hold of George’s correspondence with Mehmet and appealled to the Pope, Pius II (for whom George might have been working as an agent!), accusing George of treachery and George was imprisoned for four months in 1466-67. Released from prison, George now offered to dedicate both translation and commentary to Matthias Corvinus (1443–1490), the king of Hungary.

We now need to back peddle to 1460. In that year, Bessarion, who was a Papal legate, visited Vienna to negotiate with Frederick III and made the acquaintance of Georg von Peuerbach (1423–1461), who was at the time the leading astronomical scholar in Europe. Bessarion, still deeply upset by George’s abortive Almagest efforts, asked Peuerbach to produce a new commentary on Ptolemaeus’ work. Peuerbach acquiesced and began immediately to produce an epitome or digest of the Almagest. This was an updated, modernised, shortened, mathematically improved version of the Almagest. Peuerbach died in 1461, having only completed the first six of thirteen book of his epitome. He did, however, extract the deathbed promise from his star pupil, Regiomontanus, to finish the work. In the same year Regiomontanus left Vienna for Italy as a member Bessarion’s entourage, where he spent the next four years learning Greek, finishing the epitome and acting as Bessarion’s manuscript collector and librarian. The Epitome of the Almagestis a masterpiece:

The Epitome is neither a translation (an oft repeated error) nor a commentary but a detailed sometimes updated, overview of the Almagest. Swerdlow once called it “the finest textbook of Ptolemaic astronomy ever written.”[1]

I’ve already written an earlier blog post on Regiomontanus so we don’t need to outline the rest of his life but Shank does have an interesting hypothesis. He suggests that Regiomontanus went to Hungary at Bessarion’s behest in order to counter any influence that George might win at the Court of Corvinus through his second attempt to rededicate his Almagest and Commentary.

When he set up his printing business in Nürnberg, Regiomontanus published Peuerbach’s lectures on astronomy, Theoricae Novae Planetarum, as his first book.

Although he included the Epitome in his publisher’s prospect he didn’t succeed in publishing it before his untimely death in 1476. The Epitoma in Almagestum Ptolemae was first published in 1496 in Venice by Johannes Hamman. Together with Peuerbach’s lectures the Epitome became the standard textbooks for teaching astronomy at the European universities for much of the next century. The influence of the Epitome goes much deeper than this in the history of astronomy.

It is well known that Copernicus modelled his De revolutionibus on Ptolemaeus’ Almagest. In fact text analysis has shown that he actually modelled his magnum opus on the Peuerbach-Regiomontanus Epitome, for example taking most of his knowledge of Arabic astronomy from Regiomontanus’ work. This is, however, rather minor compared to what several expert think is the most important influence that Regiomontanus had on Copernicus.

According to ancient Greek cosmology the planets orbit the earth with uniform circular motion. Any extended observation of the planets show that this is not the case and it was the job of the astronomers to construct geometrical model, which corrected the visible deviation from the cosmological norm; these deviations are known as the anomalies. Ptolemaeus had basically two geometrical tools to describe planetary orbits. With the eccentric deferent the centre of the circle that describes the orbit, the deferent, is not in the same position as the earth, i.e. the earth is not at the centre of the planets orbit. The alternative is the epicycle-deferent model in which the planet is carried around an epicycle, which is itself carried around the deferent. The mathematician Apollonius (late 3rdcentury–early 2ndcentury BCE) had shown that the two models were in fact mathematically equivalent; meaning any motion that could be described with the one model could equally well be described with the other.

Ptolemaeus, however, argued in the Almagest that whereas the retrograde motion (the so-called second anomaly, when the planet appears to reverse its orbital direction for a period of time) of the outer planets could be described with either model that of the inner planets (Venus and Mercury) could only be described with the epicycle-deferent model. In Book XII of the Epitome, Regiomontanus proved that the second anomaly of the inner planets could also be described with the eccentric deferent model. Without going into detail this seems to have led Copernicus directly to his heliocentric system for the inner planets, which he then extended to the outer ones.

Thinking hypothetically, if George had not written his translation of and commentary on the Almagest, then Bessarion would not has asked Peuerbach to write the Epitomeand Regiomontanus might never have provided Copernicus with that vital clue.

Regiomontanus wrote a second book inspired by George’s work. His Defensio Theonis contra Georgium Trapezuntium is a vast rambling mathematical work centred on a defence of Theon of Alexandria against what he saw as George’s unfair treatment of him. He accused George as having both misrepresenting Theon and plagiarising him. This work has never been published but Regiomontanus’ antagonism against George was known at the time. The Defensio was announced in Regiomontanus’ prospect and also in works published by Erhard Ratdolt. This situation led to a rather strange claim made by Pierre Gassendi. In the 1650s Gassendi published a collective biography of the great astronomers Brahe, Copernicus, Regiomontanus etc. in which he claimed that Regiomontanus was murdered in Rome by two of George’s sons in 1476. George had many vocal critics, none of whom were murdered and sensible historians think that Regiomontanus died in one of the epidemics that regularly swept Rome.

[1]Michael H. Shank, Regiomontanus and Astronomical Controversy in the Background of Copernicus, pp. 79-109 in Rivka Feldhay and F. Jamil Ragep eds., Before Copernicus: The Cultures and Contexts of Scientific Learning in the Fifteenth Century, McGill-Queen’s University Press, Montreal& Kingston, London, Chicago, 2017, p. 90

This blog post owes much to the above paper and to Michael H. Shank, The Almagest, Politics, and Apocalypticism in the Conflict between George of Trebizond and Cardinal Bessarion, in Almagest International Journal for the History of Scientific Ideas, Volume 8, Issue 2, 2017, pp. 49-83