“I know that the Chaldaeans and Indian sages were the first to say that the soul of man is immortal, and have been followed by some of the Greeks, particularly by Plato the son of Ariston.” (Pausanias, Description of Greece 4.32.4)
Now that’s an arresting passage. An ancient author – albeit one who wrote a half-millennium after Plato’s death – stating outright that Plato derived one of his most important doctrines from India. But the fact that an ancient author claims something does not, of course, make that thing true, and very few classicists think that Plato derived any of his core doctrines from non-Greek sources.
Ancient claims to the contrary reflect an impulse as old as Greco-Roman civilization: to see the ancient cultures of the east as a source of deep, if sometimes dangerous, wisdom.
The Greeks and Romans assumed that Plato traveled widely, and there is no particular reason to doubt that he did. We don’t really know where he went since our sources about his life – with the partial exception of the spuriously autobiographical Seventh Letter – are late and unreliable. Egypt was then (depending on the time of Plato’s visit) either part of the Persian Empire or under the rule of the native 30th Dynasty.
In either case, Egypt was – though not nearly to the extent that it would be in the Hellenistic and Roman periods – connected by trade with India. It is conceivable that Plato could have encountered someone who had been to India or someone who knew someone who had.
But there is no direct evidence – in Plato’s own works or those of his contemporaries – that any Greek writing before Alexander’s conquests had a substantive understanding of Indian religion or philosophy. There were of course rumors and reports about the far east – one thinks of Herodotus’ gold-digging ants, said to live in the deserts of northern India – and a few authors active during or before Plato’s lifetime produced works purporting to describe Indian customs.
With the exception of Herodotus, these authors survive only in excerpts. They do not seem, however, to have been especially accurate; the most (in)famous of them, Ctesias, was apparently responsible for the myth of the skiapods, men who hopped around on a single enormous foot, and then (when wearied by hopping) used their feet as umbrellas as they napped. What, if anything, Ctesias had to say about Buddhism is unknown, but it is unlikely to have been inspiring.
Nor is there any internal evidence for Buddhist doctrines in Plato’s works – or so Richard Stoneman concludes in his recent book on the Greek Experience of India. There was the potential for real intellectual cross-fertilization between the Greek and Indian traditions; Stoneman, for example, thinks that the philosophy of Pyrrho of Elis was deeply influenced by Buddhism.
Pyrrho, however, was born a generation after Plato, and supposedly accompanied Alexander to India. He was, in other words, exposed to Indian philosophy in a way that only became possible in the wake of Alexander’s conquests.
During the Hellenistic period, a considerable number of Greeks in the Indo-Greek kingdoms would convert to Buddhism (the Questions of King Menander are the most famous product). But in the Mediterranean world, Buddhism remained an ill-understood religion, known – if at all – through the distorted mirror of Manicheism or the late antique fable of Barlaam and Joasaph. If Plato knew anything substantial about the Buddha or Buddhism, in other words, he kept it to himself.