Inthe Death of Socrates the subject is the symbol of the enlightenment himself: Socrates. The ancient Greeks had the first enlightenment - the struggle between superstition and reason. They were pioneers in the search for man's nature. By his death he became a martyr for truth. He chose to take the cup of poison hemlock rather than stop teaching.
In this scene Socrates takes the cup of hemlock almost casually as he continues his teaching to his mourning followers.