The Celts in ancient Britain and Ireland celebrated Halloween over 3000 years ago as a festival to mark the end of the harvest season and the beginning of winter. They believed that on October 31st, the boundary between the living and the dead became blurred and spirits of the dead returned to Earth. Modern Halloween traditions such as carving jack-o-lanterns and children dressing up and going trick-or-treating evolved from ancient Celtic rituals intended to appease or ward off these spirits.