If I recall correctly, it was written by Plato based on the witness of a person in an adjacent cell. By all accounts, he was not a charlatan. He kept talking to people about all his usual stuff and telling people to quit crying because it's not that big a deal. When the guard came with the drink, he thanked him for his troubles, and asked him how to make it work the best. The guard told him to drink it, and then walk around his cell until his legs feel heavy, and then just lay down. He downed it in one pull, paced around his cell making jokes about how he was taking this so much better than everybody else around him until he had to be helped into bed. He picked that moment to remind his main student, Crito, that he owed an animal sacrifice to Asclepius, but hadn't gotten around to it yet, and died. Legend.