On the last night of October, they gathered to celebrate their New Year's Eve festival. They lit huge bonfires and they also wore scary masks to frighten away the ghosts and goblins that were thought to walk the earth on that night.
According to the Celts, the spirits that came out on Halloween would desguise themselves and knock on doors, asking for food or presents. If the people who answered the doors didn't give out treats, the spirits would play pranks on them. This is the origin of trick-or-treating.
