Halloween's origins date back around 2,000 years to the ancient Celtic festival of Samhain, observed in areas now part of Ireland, the United Kingdom, and northern France. Samhain marked the transition from harvest to winter, a period associated with death. Celts believed the boundary between the living and the dead was blurred on the night of October 31, allowing spirits to return. To protect themselves or blend in, they lit bonfires and wore costumes.