Samhain

In the 7th century Ce Pope Boniface IV established All Saints' Day, originally on May 13, and in the following century, perhaps in an effort to supplant the pagan holiday with a Christian observance, it was moved to November 1. The evening before All Saints' Day became a holy, or hallowed, eve and thus Halloween.

The tradition originated with the ancient Celtic festival of Samhain, when people would light bonfires and wear costumes to ward off ghosts. In the eighth century, Pope Gregory III designated November 1 as a time to honor all saints. Soon, All Saints Day incorporated some of the traditions of Samhain.