Halloween, the holiday celebrated annually on Oct. 31, draws its origins from the ancient Celtic festival of Samhain, in which the Celts would light bonfires to ward off spirits.
The festival evolved over time and took on medieval Christian influences. Many modern Halloween rituals, such as carving pumpkins into jack-o’-lanterns and wearing costumes, originated from both pagan and Christian traditions.
In the eighth century, Pope Gregory III declared the first day of November to be All Hallows’ Day, to honor the saints. Thus, the day before became known as All Hallows’ Eve, which later became the Halloween we know today.
– Andrew Aston, The Oklahoma 100