For about a hundred and fifty years, some of the best minds in Europe believed that an Egyptian sage named Hermes Trismegistus had written philosophy before Moses wrote law. They were wrong about nearly everything except the importance of the books.
The story of how a god became an author, how the author became a prophet, and how one stubborn philologist took it all apart is one of the great detective stories in the history of ideas. It also explains why the word "Hermetic" still carries a charge.
A god with two passports
The figure begins with Thoth, an Egyptian god. Britannica describes him as scribe of the gods, inventor of writing and patron of every art that depends on writing, which in practice meant nearly all organized knowledge.
When Greek speakers settled in Egypt after Alexander's conquest, they did what Greeks habitually did with foreign gods and matched him to one of their own: Hermes, the messenger and guide of souls. The identification was official by the third century BCE. Thoth's temple city, Khemenu, became known in Greek as Hermopolis, the city of Hermes.
The title Trismegistus, "thrice-greatest," appears to be a Greek rendering of an Egyptian honorific that piled up the word for "great." The Rosetta Stone of 196 BCE already refers to Hermes as "the great, the great," evidently meaning Thoth.
So Hermes Trismegistus was never a man with a birthplace and a tomb. As the historian Florian Ebeling puts it, in the words of one review of his study, "Hermes Trismegistus was a fiction." He was a name under which a culture filed its wisdom.
The books that carried his name
A great many texts were filed there. Scholars sort the Hermetic writings into two piles. The technical Hermetica deal with astrology, medicine, alchemy and magic, and the oldest may go back to the second or third century BCE. The philosophical Hermetica are concerned with God, the cosmos and the human soul.
The most famous of the second group is the Corpus Hermeticum, a set of seventeen Greek treatises. Britannica dates these writings to roughly the first through third centuries CE and describes them as dialogues in the Platonic manner, blending Eastern religious elements with Platonic, Stoic and Neo-Pythagorean philosophy. A related Latin dialogue, the Asclepius, stayed in circulation throughout the Middle Ages.
Early Christian writers knew this material. Lactantius, in particular, treated Hermes as a pagan sage of great antiquity, and that reputation outlived the Roman world.
Florence, 1463: Plato can wait
The Greek Corpus was unavailable to Latin readers for centuries. Then a manuscript arrived in Florence from Macedonia, brought by one Leonardo da Pistoia, and came into the hands of Cosimo de' Medici.
Cosimo had recently commissioned the young scholar Marsilio Ficino to translate the complete works of Plato into Latin. Now Cosimo told him to set Plato aside and do Hermes first. Ficino finished in 1463. It was his first major work.
The priority tells the whole story. Ficino and his patron believed in a single ancient theology, a chain of sages running from Hermes in Egypt through Orpheus and Pythagoras to Plato. On that view Hermes was the source and Plato a late heir, and here was the source itself.
Ficino's Latin version, known as the Pimander after its first treatise, was printed at Treviso in 1471, reportedly without his knowledge. In 1488 the cathedral of Siena set Hermes into its marble floor, the first panel a visitor meets inside the door, honoring him as a founder of human wisdom. A pagan sage had been welcomed into a Christian church.
Casaubon reads the Greek, and the desert answers
The welcome ended in 1614. Isaac Casaubon, one of the finest classical scholars of his age, took up the Hermetic texts in the course of the religious controversies of his day, and he read them the way a philologist reads everything, with close attention to language.
What he found was Greek that was too late. The vocabulary, the style and the ideas belonged to the centuries after Plato and after the rise of Christianity, not to the age of the pyramids. A book that echoed Plato and the Gospels had been written by someone who had read them, not by someone who foresaw them. Casaubon placed the texts in the early Christian era, and modern scholarship has broadly confirmed his dating.
It was a landmark in critical method: a revered document dated by internal evidence alone. Hermetic philosophy lost its standing in learned circles, though alchemists and esoteric groups carried on largely undisturbed.
Casaubon settled the date, but his verdict hardened into something he had not strictly proven: that the Hermetica were a mere Greek forgery with nothing Egyptian in them. The twentieth century complicated that.
In 1945 a farmer digging near Nag Hammadi in Upper Egypt uncovered a cache of fourth-century papyrus books written in Coptic, the last stage of the Egyptian language. Most of the texts were Christian, but one codex contained Hermetic works: part of the Asclepius, a prayer of thanksgiving, and a previously unknown dialogue now called the Discourse on the Eighth and Ninth, in which Hermes guides a pupil through a visionary ascent.
Here was evidence that Hermetic texts were being copied and read in Egypt, in Egyptian, alongside Christian scripture. Later research, notably by the French scholar Jean-Pierre Mahé, found continuities with older Egyptian wisdom literature, and raised the possibility that the earliest Hermetica came from Hellenized members of the Egyptian priesthood.
The author who never lived
The honest answer to the title question has three parts. Hermes Trismegistus was a fusion of two gods. He was also a pen name used by anonymous writers in Roman Egypt who thought in Greek and felt Egyptian. And he was a Renaissance mirage, a prophet older than Moses who existed only in the hopes of his readers.
The first two are history. The third was an error, and a fruitful one, because it sent Europe's scholars back to study antiquity with fresh urgency. Hermes never wrote a word, and the books under his name changed the world anyway.