Aristides a most eloquent Athenian philosopher, and a disciple of Christ while yet retaining his philosopher's garb, presented a work to Hadrian at the same time that Quadratus presented his. The work contained a systematic statement of our doctrine, that is, an Apology for the Christians, which is still extant and is regarded by philologians as a monument to his genius.
Source: De Viris Illustribus (Illustrious Men) (New Advent)