What did thew Celts believed happened on the last day of october?

The Celts believed that on the last day of October, specifically during the festival of Samhain, the boundary between the living and the dead became blurred. They thought that on this night, the spirits of the deceased could return to the earth, leading to a celebration that honored them. To ward off malevolent spirits, people would light bonfires and wear costumes, practices that have influenced modern Halloween traditions. This time was also seen as a transition into winter, marking the end of the harvest season.