This once pagan holiday was made into a Christian festival from the efforts of Pope Boniface. Initially, these holidays were celebrated on May 13. A century later, it was changed to November 1st by Pope Gregory III. This is how it remains to this day. This meant October 31st was not the last day of the year any longer, and Samhain was changed to The Feast of All Saints. October 31st was the day when summer officially ended for 5th century BC Ireland. It was believed by the Celts that ghosts walked among the living on this day. They called this holiday Samhain. It was the time of the third and last harvest of the year. It was also the Celtic New Year. The Celts observed this day as their New Year most likely because the sun is at its lowest point on the horizon. This was measured by Britain and Ireland’s ancient standing stones.