Halloween was originally a pagan holiday, honoring the dead. Halloween was referred to as All Hallows Eve and dates back to over 2000 years ago.
Samhain was the Druids holiday celebrating the end of summer based on a lunar calendar. The holiday started on sunset of October 31st the last day of the Celtic calendar.
The ancient Druids, druid means priest of the oak, were the learned priestly class of the Celtic religion that were in existence from 200 BC to about 350AD. They believed in reincarnation, and the transmigration of the soul, which teaches that people may be reborn as animals.