Who were the Celts that served as priests, judges, and teachers?
Along with kings and chieftains, Druids were the most revered people in the Celtic societies, based primarily in modern-day France, Ireland, and Britain. Because the Celts did not use a written language, Druids learned by oral tradition, passed down through the generations. They were known for their interest in both nature and prophecy, and they handled legal, political, and sometimes medical issues.
Source: Britannica