Halloween originated from the ancient Celtic festival of Samhain, celebrated on November 1st. The Celts believed the boundary between the living and the dead became thin on Samhain, allowing spirits to walk the Earth. People wore costumes and carved lanterns from turnips and potatoes to ward off spirits. When Irish immigrants arrived in America in the 1800s, they brought their Samhain traditions, carving pumpkins instead of turnips and celebrating Halloween. Trick-or-treating evolved from the medieval tradition of souling, where poor people would beg for food in exchange for prayers for the dead.