According to the Celtics' mythology, with the coming of winter, which is a season of the dead, came a night in which the spirits of the dead could freely roam about with humans. Some of these spirits would inflict suffering and violence upon man. To calm down the spirits and the gods that were worshipped, the Celtic people would put out their best food offerings on the doorstep and also used to offer sacrifices, animal and human.
The Celtic people prayed to the gods to ask for a return of the sun and in hopes that the gods would chase away the evil and frighten away the spirits. Often, they used to wear dreadful costumes, hoping to fool an evil spirit with the disguise. These are some of the practices and origin of Halloween that are still being practiced today.