The festival of Samhain marked the end of the light half of the year and the beginning of the dark. As well as celebrating the harvest it was believed that on this night the spirits of those who had died that year walked the earth. People would extinguish fires to make their homes unwelcoming to spirits and dress up and make noises to frighten away the ghosts.

Druids would visit homes, offering prayers against possession in exchange for food and gifts. If gifts were not offered then the druids would curse them instead - the original trick or treat.

Why we have Jack-O-Lanterns:

Legend has it that in the 18th Century an Irish blacksmith named Jack was banned from entering Heaven for colluding with the Devil.

Damned to walk the earth Jack asked the Devil for light and was given a burning coal ember which he placed in a gouged out turnip. Making a lantern from hollowed turnips on All Hallow's Eve became a tradition in Ireland. When Irish emigrants arrived in America in the 1840s they had no turnips but found pumpkins a better alternative for making the Jack-O-Lanterns...