This Halloween shirt is celebrated every year on October 31st, and Halloween 2021 will happen on Sunday, October 31st. The tradition originated with the ancient Celtic festival of Samhain when people would light bonfires and wear costumes to ward off ghosts. In the eighth century, Pope Gregory III set November 1 as the date to honor all saints. Soon after, Halloween incorporated some Samhain traditions. The night before was known as All Hallows Eve, and later as Halloween. Over time, Halloween has evolved into a day of activities such as trick-or-treating, lantern carving, festive gatherings, dress-up, and eating.