The Celtic festival of Samhain began about 2,000 years ago in what is now Ireland. It marked the end of summer and the harvest, and the start of winter. The Celts believed that on October 31, the day before All-hallows (also known as All Saints' Day), the ghosts of the dead returned to earth. Around 800 A.D., Samhain began to be called All-hallows Eve and, eventually, Halloween.