Plato Plato 
Protagoras 

The Protagoras, like several of the Dialogues of Plato, is put into the mouth of Socrates, who describes a conversation which had taken place between himself and the great Sophist at the house of Callias-‘the man who had spent more upon the Sophists than all the rest of the world’-and in which the learned Hippias and the grammarian Prodicus had also shared, as well as Alcibiades and Critias, both of whom said a few words-in the presence of a distinguished company consisting of disciples of Protagoras and of leading Athenians belonging to the Socratic circle.