A member of the ruling caste of the Gallic Celts. Knowledge of the Druids is derived chiefly from the hostile accounts of them in the Roman authors Julius Caesar and Tacitus. Caesar reports that they exercised judicial and priestly functions, worshipped in groves (clearings in forests), and cut mistletoe from the oak tree (sacred to them) with a golden sickle. The religion was stamped out by the Romans, to prevent its resistance to Roman rule.