"George Gemistos Plethon was a crypto-Pagan." (An Inconvenient Pagan, Part Three)

1.
Church and Society in the Last Centuries of Byzantium, Donald M. Nicol, 1977

"George Gemistos Plethon was surely the least representative of all the Byzantines at Florence. Like Bessarion he was interested in bridging the intellectual and cultural gap between Greeks and Latins. But in him the wind of Hellenism blew so strong that it extinguished his Christian faith. The proceedings of the Council of Florence confirmed his opinion that the only hope for the world was to dispense with Christianity altogether and to evolve a completely new philosophy of life and politics. It was at Mistra in Greece, far away from the beleaguered capital, that Plethon developed his ideas for the regeneration of what he was pleased to call the Hellenic people. This was to be acheived not by breathing new life into the dying body of the Roman Empire but by a reform of society along the lines suggested in Plato's Republic. Early in the fifteenth century Plethon addresed to the Emperor Manuel II and his son Theodore a series of memoranda on the ways in which Hellenism could be recreated on the Hellenic soil of the Peloponnese. They amounted to an elaborate and comprehensive programme for the reform of the administration, the defense of the economy and the structure of society. They contain some of the most original ideas eer expressed by a Byzantine scholar. But far more strikingly - and more dangerously - original were Plethon's ideas on religion, which he committed to writing late in his life in a treatise called On the Laws. Here he concocted a new "Hellenic" religion worthy of credence by his regenerated Hellenes. The myths of Christianity were to be supplanted by an artificial theology and ethical system based on Plato and neoplatonism. God reverted to being Zeus and the rest of the ancient Greek pantheon were suitably accommodated as the new presiding deities. The treatise was never published ; and when the text came into the hands of Plethon's friend, the Patriarch Gennadios, he considered it his duty as a Christian to destroy it."
[pp. 113-114]

2.
Byzantium: Church, Society, and Civilization Seen through Contemporary Eyes, Deno John Geanakoplos, 1984

"In the fifteenth century several Byzantine thinkers attempted to reform the existing calendar by developing one that corresponded more closely to the rotation of the earth and movement of the planets than the Julian calendar. Among these was the famous Neoplatonic philosopher (and rejector of Christianity) Gemistus Pletho .... The greatest of Byzantine philosophers, Pletho, held views remarkable for his time. Deeply disturbed (as were many other intellectuals) over the terrible condition of the empire, he sought to revive the Byzantine state. One means he proposed was the replacement of traditional Christianity with Paganism."
[pp. 435-43]

3.
The Last Centuries of Byzantium, 2 ed., Donald M. Nicol, 1993

"Plethon would have agreed that a change of heart was needed if the Byzantines were to live up to the ideal of Hellenes. But his thoughts led him further and further away from any expectation that this could come about through the medium of the Christian faith. Not until towards the end of his life did he commit these thoughts to writing in a treatise called On the Laws. In this he was to advocate a total rejection of Christianity in favour of a new 'Hellenic' religion, incorporating the pantheon of ancient Greek gods and based on a theological and ethical system derived mainly from Plato but also from Zoroaster. Little is known of this work, for it was consigned to the flames as an atheistical and dangerous tract by Plethon's friend George Scholarios, after he became Patriarch."
[p. 345]

4.
"Gemistus Plethon and Platonic Political Philosophy", Peter Garnsey, in Transformations of Late Antiquity: Essays for Peter Brown, edited by Philip Rousseau and Manolis Papoutsakis, 2009

"Plethon was a crypto-Pagan: he dreamed of introducing a new religion based on wisdom that was older than Christianity and Islam, namely a blend of Zoroastrianism, Pythagoreanism and Platonism. In respect of his religious and philosophical beliefs, Plethon belongs in the tradition of the Neoplatonist philosophers of Late Antiquity."
[p. 328]

5.
A History of Byzantium, Timothy E. Gregory, 2010

"Plethon was not the first of the Byzantines to point out the connection between Byzantine and ancient Greek culture, but he put that point eloquently and clearly. 'We are,' he wrote, 'Greeks [Hellenes], as our language and ancestral culture show.' Thus, to Plethon, as to many Byzantines, Greekness was not a matter of blood or descent, but rather determined by language and culture. Plethon was also willing to call himself a Hellene, the term that had long been used by the Byzantines to refer to Pagans. This did not trouble him and, unlike most of his contemporaries, he was unabashedly in favor of the (certainly impossible) task of restoring classical Paganism as the religion of the empire!"
[pp. 386-387]