Halloween originates from the ancient Celtic festival of Samhain, celebrated about 2,000 years ago, primarily in Ireland and parts of Britain. Samhain marked the end of the harvest season and the beginning of winter, a time when people believed the boundary between the living and the dead was thinnest, allowing spirits to pass through. During Samhain, bonfires were lit, and people wore costumes or masks to ward off or disguise themselves from harmful spirits. In the 8th century, the Christian church established November 1 as All Saints' Day (All Hallows), with the evening before called All Hallows Eve, eventually shortened to Halloween. The holiday incorporated some of the older Celtic customs while adapting to Christian traditions. Irish immigrants carried these traditions to America, where Halloween evolved into the modern celebration involving trick-or-treating, costume parties, and pumpkin carving (originally turnips in Ireland). Thus, Halloween has roots mainly in Celtic paganism with later Christian influences shaping the holiday as known today.