The Druids, ca. 54 BC
Their history is cloaked in mystery. The ancient Druids were members of the priestly class of the Celtic society that originated in Britain and migrated to what is now central France. The Druids occupied a revered social status among the Celts due to their service to the community as priests, teachers, diviners, and magicians. Two of the significant attributes of the Celtic religion were the veneration of the oak tree and the ritual of human sacrifice in ceremonies supervised by the Druids.
Among the major religious tenants emphasized by the Druids was the belief in the immortality of the soul. Historians, however, are unclear as to how this immortality was actually realized. Some posit that the Druids taught that the soul escaped the deceased’s body at death and immediately occupied the body of a living person. Others declare that the Druids believed that the human soul escaped the body at death to forever occupy an Otherworld similar to that experienced by the deceased in life.
http://www.eyewitnesstohistory.com/druids.htm
