What is the main idea? Before you put on that skeleton costume and rove door-to-door pandering for candy, take a minute to reflect on this tradition. Halloween is believed to have come from an ancient Celtic festival dating back some 2,000 years. November 1st was the Celtic New Year and marked the end of summer to the Celts. They celebrated on its eve by wearing costumes made of animal skins and dancing around bon fires. Over the next two millennia, this primitive celebration grew to be the candy fueled costume ball that we know today.