Celtic Beginnings
History shows that Halloween originated in ancient Britain and Ireland (5th century BCE), on the full moon closest to November 1st.
This is when the Celts celebrated the festival of Samhain - Summer's End, the Celtic New Year.
Samhain was the god of the dead. They believed that the barrier between the physical and the spirit world disappeared and that the spirits of the dead, good and evil, returned to earth.
These spirits would harm people if not offered gifts, such as food and drink, and sweet goods. People would often dress as spirits so that evil spirits would not recognize them.
As it marked the end of summer, it was necessary to perform various rites and sacrifices to awaken the dying sun.
All fires were extinguished, sacred fires were lit for the new year, and these people lit new fires in their homes, to safeguard them during the approaching winter.
These sacred bonfires would repel evil spirits, and they were also used to offer crop and animal sacrifices to Celtic deities.
Druids, and Celtic priests, wore animal-skin customs and told each other's fortunes. Druids went from house to house, carrying lanterns and demanding money as offerings.
Samhain was also celebrated for indulging in drunkenness and otherwise forbidden conduct in daily life.
Roman Rule
From 43 CE onwards, the Romans ruled the Celts. Roman customs were merged with Celtic traditions.
For example, the goddess Pomona was a goddess of fruit, trees, and fertility. Apples and hazelnuts were considered sacred and used for divining information on marriage, childbearing, and death - very important questions in an agricultural community.
Apples with certain markings were placed in a tub of water or hung from a tree. By grabbing one dela using only the mouth, a young man or woman was supposed to be able to foretell his or her future spouse.
Christianity
Christianity then spread to Celtic lands. In the 7th century, Pope Boniface IV is said to have designated May 13 as a time to honor all martyrs - All Martyrs Day.
In the 8th century, Pope Gregory III chose November I instead to honor martyrs, saints, and relics as well.
All Saints' Day incorporated some of the traditions of Samhain. All Souls' Day came after All Saints' Day.
The All Saints' Day celebration was also known as All-hallows or All-hallowmas, and the night before it, the same night as Samhain, began to be called All-Hallows Eve and, eventually, Halloween, from the 18th century onwards.
The Christian church also urged its followers to dress like spirits, angels, and devils to go from house to house and request small goods, such as food, in exchange for prayers for dead relatives, “going-a-sou ling”. One particular treat handed out was called a soul cake, a traditional cookie with a cross on the top.
Candles or burning coals were placed in carved-out turnips or other root vegetables and were carried or placed in windows to repel Stingy Jack (a fabled drunken man doomed to roam the earth by Satan) or other spirits.
Later, this was also thought to represent a soul trapped in purgatory. Pumpkins were used instead when the custom was brought to America.
The New Catholic Encyclopedia notes that “throughout the Middle Ages it was a popular belief that the souls in purgatory could appear on this day as will-o'-the-wisps, witches, toads, etc.”