Today is the last day of October, which means it’s time for creepy costumes and pounds of candy. Halloween is a favorite among many, but most people are oblivious to the history behind the holiday.

According to ancient legend, the origin of Halloween dates back 2,000 years ago to the ancient Celtic festival of  Samhain. The Celts, who lived in the area that is now Ireland, the U.K. and northern France, celebrated their new year on November 1. It marked the end of their summer and harvest, and the start of the cold, dark winter, which was associated with death. The Celts believed that on October 31st, the boundary between the worlds of the living and dead was temporarily blurred. They celebrated Samhain on the night of October 31st, when people thought the ghosts of the dead returned to earth.

Pope Gregory III turned November 1 into All Saints’ Day, a time to honor saints and martyrs. The night before was called All Hallows Eve, and later, Halloween.

Although its background was originally holy, over the years it somehow got a bad reputation. People began to think that dressing up like ghosts was not to honor the dead, but to summon demons, which is why many people today don’t celebrate Halloween. Nowadays, society has created their own Halloween traditions, like wearing costumes and trick-or-treating, turning the once sacred holiday into a day for fun and laughter.