The term Halloween is shortened from All-hallow-even, as it is the before "All Hallows' Day" ( also known as "All Saints' Day" ). The holiday was a day of religious festivities in various northern European Pagan traditions, until Popes Gregory IV moved the old Christian feast of All Seints Day from May 13 to November 1. In the ninth century, the Church measured the day as starting at sunset, in accordance with the Florentine calendar. Although we now consider All Saints' (or Hallows') day to be on the day after Halloween, they were, at that time, considered to be the same day.