George Gemistos (who late in life changed his surname to Plethon, another way of connoting “full” in Greek) was born, probably in Constantinople, sometime after 1355. He died at Sparta nearly a century later. As a young man he went to Adrianopolis, at that time the Turkish capital and a center of learning, for Sultan Murat, promoting the arts, followed the model of the caliphates of Cairo and Baghdad. Here one Judaeus Elissaeus initiated Gemistos into the mysteries of Zoroaster. After his teacher was burned at the stake for heresy, Gemistos left Adrianopolis and journeyed to Cyprus, Palestine, and other places, ending up at the Byzantine fortress of Mistra, just outside Sparta, in the Peloponnese. Here he began to teach and write philosophy. Among his pupils were the future Cardinal Bessarion and George Scholarios, eventually to be Patriarch Gennadios of Constantinople. Gemistos composed historical, geographical, and astronomical works and drafted digests (summaries) of many classical writers. Theodore, despot of Morea (i.e., the Peloponnese), made him chief magistrate. In 1415 he directed letters to Emperor Manuel Paleologus and to Theodore with ideas for political, legal, and economic reform. His reputation as a legal thinker spread. Some of his contemporaries claimed that he carried legal codes in his memory. His main work on laws, Nómon singrafí, was apparently carried in manuscript to Constantinople by the wife of the despot of Morea and burned at Scholarios's injunction after Gemistos's death. Only a few sections of Nómon singrafí, quoted or copied, survive. In them Gemistos appears to merge the teaching of the Stoics with the esoteric of Zoroaster, propounding mystical theories like astrology, the influence of demons, and the migration of human souls. His doctrinal enemy, Scholarios, apparently preserved certain fragments of this peripatetic masterpiece before destroying it.
Gemistos interpreted the gods of ancient Greece as metaphysical principles.