Like Greeks and Romans, barbarians worshipped hundreds of gods and goddesses with specialized functions. They regarded certain mountains, lakes, rivers, or groves of trees as sacred because these were linked to deities. Rituals to honor the gods were held outdoors rather than in temples or churches, often at certain points in the yearly agricultural cycle. Presided over by a priest or priestess, rituals sometimes involved animal (and perhaps human) sacrifice. Among the Celts, religious leaders called druids (DROO-ihds) had legal and educational as well as religious functions, orally passing down laws and traditions from generation to generation. Bards singing poems and ballads also passed down myths and stories of heroes and gods, which were written down much later.