Halloween has its origins in the Celtic holiday of Samhain, celebrated on October 31st to mark the end of the Celtic year and the division between the living and dead. The Celts believed that on Samhain, the boundary between the living and the dead became blurred and the dead could return to Earth. To appease spirits and avoid having them enter their homes, Celts would decorate with bones and skulls, giving rise to our modern traditions of costumes and home decorations for Halloween.