The holiday of Halloween has roots that trace as far back as the ancient Celtic festival of Samhain (pronounced sow-in). The purpose of the festival was to mark the end of summer and the harvests of the year and the beginning of the shorter days that were much colder and darker as they came with winter. Winter because it was often dark and extremely cold was thought to somehow be associated with human death. The Celts believed that the night before November 1st (the day that was the beginning of their new year) the veil between the human world of the living and the spirit world of the dead was very thin, even blurred. The Celts celebrated the festival of Samhain on October 31st. The Celts believed that ghosts would return to earth and communicate with the living. Some ghosts would cause mischief including damaging crops and pull pranks on the living which in turn would cause other kinds of trouble. The Celts also felt that the Druids and seers would be in a better position to talk to the spirits and make more accurate predictions for the upcoming year. Because the Celts were so connected to their natural world for any level of survival, the predictions provided to the community by the Druids were a big source of comfort to help them through the cold, darkness of winter.
The night of the Samhain celebration, the Druids would built large bonfires where sacrifices of crops and animals were made to the Celtic Gods. During this time the people wore costumes and would attempt to tell each others fortunes. When the evening was over the Celts would relight their own fireplace hearts with a flame from the large sacred community bonfire. It was the superstitious belief that lighting the hearth from that flame would keep the family protected through the approaching winter season.
Over the next several centuries, the traditions of Samhain were combined with Roman and Christian holidays to make up the holidays of All-Hallows (All Saint's Day held on November 1st) and All-Hallows Eve (held on October 31st). All Hallows Eve ever became known as Halloween.