Contrary to many people’s perception of him, Plato did not spend his entire life listening to Socrates philosophising in colonnades in Athens or writing dialogues meandering through complex ideas. He was once captured in the middle of the Mediterranean Sea and put up for sale in a slave market. The reason we seldom hear about this is the same reason there hasn’t been a stand-alone biography of Plato in English in nearly 200 years. The sources for his life are untrustworthy and fiendishly difficult to interpret.

The enslavement allegedly occurred while Plato was travelling home from Sicily in 384 BC. A number of ancient biographers claim that the philosopher boarded a ship with a Spartan who enslaved him on the orders of the tyrant of Syracuse, but Plato’s new biographer, Robin Waterfield, suggests it’s more likely that he was on board a merchant ship which caught the eye of pirates. The seas were full of marauders in this period and it is entirely possible that Plato sailed into treacherous waters. His luck changed after he was spotted in the market by an admirer who agreed to pay a ransom to secure his release.

Plato never mentioned any of this in his own writings, but then he rarely wrote about himself at all. The modern biographer must piece together clues from his works of philosophy, snippets of information provided by biographers and historians living centuries after he died and a small collection of letters and epigrams which are for the most part spurious. Waterfield is reluctant to dismiss the episode of Plato’s capture as pure fallacy because the circumstances are credible and the chronology seems to fit with what we know of his movements. If the story is true, it offers just a taste of what we may be missing.

Waterfield is open about the paucity of information on Plato’s life and is highly cautious in his reading of the sources and extraction of details, pirates aside. He remains wary, for example, of romantic tales of Plato’s travels to meet philosophers and seers. Tradition holds that the philosopher went to Libya to stay with a mathematician, to Egypt to study with priests, to Phoenicia to meet the Magi and to southern Italy to live with the Pythagoreans. ‘The fact that no two sources give Plato the same itinerary’, Waterfield argues, ‘shows that they are basically making it all up.’

And yet Plato did travel, including to Pythagorean Italy and, of course, Sicily. His time with Dionysius II, ruler of Syracuse, is not well documented, but Waterfield cleverly draws out what he can to evoke the spirit of philosophical mania that gripped the court during his visits. His account of Plato’s failure to reform the tyrant and establish a new constitution for him is particularly well done.

While the cautious approach is sensible, it does not always make for the most exciting story, since much of the colour of Plato’s life as we have come to know it lies in the strange, outlandish tales woven about him for reasons that can only be guessed at. It was said, for example, that Plato was either the product of a virgin birth (he was actually his mother’s fourth child) or the offspring of Apollo, god of prophecy and poetry. As a baby, his lips supposedly attracted Apollo’s bees and his mouth was filled with their honey. Later, on the eve of meeting the teenage Plato for the first time, Socrates dreamed that he was holding Apollo’s bird, a young swan, which found its wings and flew away singing. The next day, Socrates recognised Plato as the bird of his dream.

Depending on whom you read, Plato was celibate or libidinous, power-hungry or servile, normal or a little bit weird, with a ravenous appetite for olives. Waterfield understandably struggles to conjure a portrait of Plato’s personality out of such contradictory material, though his descriptions, such as that of the philosopher’s sense of humour – ‘understated, that of Cervantes rather than P G Wodehouse’ – help to nudge his narrative into the biographical genre and make this more than a work of intellectual history.

Waterfield probably rightly dismisses as slander the popular anecdote that ‘Plato’ was a sobriquet devised as a jibe at the philosopher’s beefy physique. The word could connote fatness or stockiness, either of which might have applied to Plato, even if he wasn’t enamoured of olives, but it was also a standard name in Greece. It is impossible to tell how rotund he really was from surviving portraits, which end at the shoulders.

Fortunately for Waterfield, as far as Plato’s origins are concerned, the truth is almost as interesting as the fictions. His father, who died either before or shortly after he was born, was descended from celebrated statesmen and, so he told people, the sea god Poseidon. His mother, scion of another well-heeled dynasty, later married an uncle to keep the money in the family. Her new husband owned peacocks.

Plato’s birth is traditionally given as 428/7 BC, but Waterfield makes a strong case for pushing the date forward to 424 BC or later on the basis that there is no evidence of him fighting in the final battles of the Peloponnesian War, as he would have done had he been old enough. He was probably born on Aegina in the Saronic Gulf but taken to Athens to grow up after the Athenians seized the island during the war.

Our main interest in Plato’s adult life lies in his establishment of what Waterfield calls ‘the ancient world’s most successful institute of higher education and research’. Students at Plato’s Academy studied everything from politics and logic to physics and optics and were encouraged to disagree with each other. Waterfield evokes its atmosphere superbly. Indeed, the passages on Plato’s teachings, his dialogues and his contribution to the field of philosophy are a particular strength of the book and help to compensate for the unavoidable patchiness of the biography itself. Plato ‘created a philosophy that was capacious enough to include contradictions and yet remain intact,’ he writes. The survival of Plato’s thoughts and words is perhaps all that really matters.