Halloween originated from the ancient Celtic festival of Samhain, celebrated on October 31st. The Celts believed this was the day when the boundary between the living and the dead was at its thinnest. They would wear costumes and light bonfires to ward off spirits. The Roman Catholic Church later designated November 1st as All Saints' Day and incorporated aspects of Samhain celebrations into it. Today, Halloween traditions include wearing costumes, trick-or-treating, and carving pumpkins, which originated from the Celtic tradition of carving turnips to ward off evil spirits.