When did Halloween start?

The Celts of Ireland, Britain and northern France celebrated Samhain more than 2,000 years ago, believing the boundary between the living and the dead grew thin as winter began. People lit bonfires and wore disguises to ward off wandering spirits. In the 8th century Pope Gregory III set 1 November as All Saints' Day, and the evening before became known as All Hallows' Eve, later shortened to Halloween. Irish and Scottish immigrants carried the customs to North America in the 19th century, where trick-or-treating grew popular in the early to mid 20th century. Today Americans spend more than 10 billion dollars a year on Halloween.