Iamblichus & The Souce Of Plato's Knowledge

Iamblichus (c. ad 242-327), a founder of Neoplatonism, tell us where Plato received much of his knowledge.

The Egyptian Hermes: A Historical Approach to the Late Pagan Mind
By Garth Fowden

http://www.granta.demon.co.uk/arsm/jg/tris.html
The Hermetists, while insisting that their compositions had indeed been written in Egyptian, and inscribed on stelae in hieroglyphic characters, were also well aware that they could not have been rendered into Greek without losing the authority that attached to sacred texts in the native language-'for the very quality of the sounds and the [intonation] of the Egyptian words contain in itself the force of the things said'.[109] A translation would require, at the very least, the active assistance of the priestly guardians of the originals. Iamblichus, for example, records that an Egyptian priest named Bitys was supposed to have translated some of the hieroglyphic texts of Thoth into Greek, and had made use of (Greek) philosophical vocabulary in doing so.[110] These texts Bitys had found 'in temples at Sais in Egypt', which of course is where Solon was supposed to have encountered Egyptian priests more learned in the history of Greece than any Greek, and to have translated parts of their archives.[111] Iamblichus also tells us that Pythagoras and Plato, during their visits to Egypt, 'read through' the stelae of Hermes with the help of native priests.[112] Whether these stories are true is not important for this discussion. What is important is first, that the Hermetists wished it to be believed that their compositions were books of Thoth rendered from Egyptian into Greek; and secondly that the legitimacy and prestige of these books depended on the finding of a plausible explanation of how this translation had been brought about. Hence the last twist in the evolution of the myth of the Egyptian Hermes, namely the presentation of none other than Hermes the younger as the translator of the Thoth texts. At any rate, this appears to be the idea underlying the obscure and corrupt pseudo-Manetho passage already mentioned. After referring to the hieroglyphic texts inscribed by Thoth, the first Hermes, pseudo-Manetho goes on to assert that 'after the Flood they were translated from the sacred language into Greek, and deposited in books in the sanctuaries of Egyptian temples by the second Hermes, the son of Agathos Daimon and father of Tat.[113] That the Thoth-literature was believed to have been rendered into Greek at such an early date has struck modern scholars as so improbable that they have emended the passage.[114] However, Plato had spoken of the translation of Greek records into Egyptian after the deluge(s); and anyway this was exactly the sort of claim that Hermetists had to make if they were to overcome the well-known inadequacies of translations from Egyptian into Greek.