On Liberty by John Stuart Mill Chapter 2 Page 26

This acknowledged master of all the eminent thinkers who have since lived — whose fame, still growing after more than two thousand years, all but outweighs the whole remainder of the names which make his native city illustrious — was put to death by his countrymen, after a judicial conviction, for impiety and immorality.

Impiety, in denying the gods recognized by the State; indeed his accuser asserted (see the “Apologia”) that he believed in no gods at all. Immorality, in being, by his doctrines and instructions, a “corrupter of youth.” Of these charges the tribunal, there is every ground for believing, honestly found him guilty, and condemned the man who probably of all then born had deserved best of mankind, to be put to death as a criminal.