Gianni Dagli Orti / Corbis

Asklepios heals a patient in the presence of his daughter Hygeia, in this fourth-century B.C. stela from the entrance to the sanctuary of Asklepios in Piraeus, Greece. The particular sort of healing that occurred in Asklepions is called incubation; patients would fall asleep, and Asklepios would then appear in their dreams to cure their ailments.