It originated on the territory of Ireland with Celtic tribes and was called Samhain (which is pronounced "Saw-win"). The word "Samhain" translates as ‘summer’s end’ and the festival marked the changing of the seasons when the harvest was over and winter was beginning.

The weight of the harvest pressed on the ground no more, making it light and easy for spirits to infiltrate from the Underworld.

It was necessary for people to light bonfires and wear costumes to ward off ghosts and spirits. Thus, we now have candles and costumes.

Food was left outside to pacify the spirits, hence trick or treating.