2909529 Democritus and Protagoras, 1663-1664 (oil on canvas) by Rosa, Salvator (1615-73); 185x128 cm; State Hermitage Museum, St. Petersburg, Russia; (add.info.: Protagoras (c. 490 ??c. 420 BC) was a pre-Socratic Greek philosopher and is numbered as one of the sophists by Plato. In his dialogue, Protagoras, Plato credits him with having invented the role of the professional sophist.); Italian, out of copyright.