The Celtic festival commonly associated with Halloween’s origins is Samhain. This Gaelic festival marked the end of the harvest and the beginning of winter, traditionally observed around October 31 and November 1 in Ireland, Scotland, and the Isle of Man.
Samhain was viewed as a liminal time when the boundary between the living world and the supernatural realm was unusually thin. Folklore held that spirits, fairies, and the dead might move among humans, helping explain later Halloween customs involving disguises, supernatural figures, bonfires, and fortune-telling.
Halloween’s name comes directly from “All Hallows’ Eve,” the evening before All Saints’ Day, so its history is a blend of Christian observance and older Gaelic traditions. Historians generally describe Samhain as a major influence rather than claiming every modern Halloween custom came directly from one ancient ceremony. The festival’s name is often pronounced roughly “sow-in,” though pronunciation varies by language and region.