When did druidism start?

Druidism, as a spiritual and religious practice, is believed to have originated among the Celtic tribes in ancient Europe, particularly around the 3rd century BCE. The Druids, who were the priestly class, played a central role in Celtic society, serving as religious leaders, advisors, and educators. Although much of what we know about Druidism comes from Roman accounts and later interpretations, its roots are deeply tied to the ancient traditions and beliefs of the Celts. The precise timeline is unclear, as Druidic practices were largely oral and not systematically documented.