Historical Origins The holiday’s earliest roots are commonly traced to Samhain, an ancient Celtic festival among peoples in Ireland, Britain, and parts of northern France. It marked the end of the harvest and the beginning of winter (roughly October 31–November 1). The Celts believed the boundary between the living and the dead grew thin at this time, allowing spirits, fairies, and other beings to cross over. Customs included lighting bonfires, wearing disguises or costumes t