What did the Celts celebrate on october 31?

On October 31, the Celts celebrated Samhain, a festival marking the end of the harvest season and the beginning of winter. It was believed that on this night, the boundary between the living and the dead was blurred, allowing spirits to return to the earthly realm. People would light bonfires and wear costumes to ward off any malevolent spirits, as well as honor their deceased ancestors. Samhain is often considered a precursor to modern Halloween traditions.