Protagoras

Protagoras is a dialogue of Plato. The main argument is between the elderly Protagoras, a celebrated sophist, and Socrates. The discussion takes place at the home of Callias, who is host to Protagoras while he is in town, and concerns a familiar theme in the dialogues: the teachability of virtue. The dialogue is perhaps most remarkable for the sheer number of people said to be in attendance: a total of twenty-one are named as present.

— Excerpted from Wikipedia, the free encyclopedia.