What was the original purpose of wearing costumes on Halloween?

Carving pumpkins, trick-or-treating, and wearing scary costumes are some of the time-honored traditions of Halloween. Yet, the Halloween holiday has its roots in the ancient Celtic festival of Samhain (a Gaelic word pronounced “SAH-win”), a pagan religious celebration to welcome the harvest at the end of summer, 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 saints. Soon after, All Saints Day came to incorporate some of the traditions of Samhain. The evening before All Saints Day was known as All Hallows Eve, and later, Halloween. Here is a look at the origins of some of the classic Halloween traditions we know today.

Source: Library of Congress