Halloween originated in the British Isles (among the Irish Celts, Scots and Anglo-Saxons in Britain long before the Christian era) out of the Pagan Celtic celebration of Samhain (end of summer). It goes back as far as 5 B.C. It was believed that spirits rose from the dead and mingled with the living on this day. The Celts left food at their doors to encourage good spirits and wore masks to scare off the bad ones.
The name “Halloween” is a shorter form for the Gaelic name All-hallow-evening. Pope Boniface IV instituted All Saints' Day in the 7th century as a time to honor saints and martyrs, replacing the pagan festival of the dead. In 834, Gregory III moved All Saint's Day to Nov. 1, thus making Oct. 31 All Hallows' Eve ('hallow' means 'saint').
The modern name, Halloween comes from "All Hallows' Evening," or in their slang "All Hallow's Even", the eve of All Hallows' Day. "Hallow" is an Old English word for "holy person," and All Hallows' Day is just another name for All Saints' Day, eventually, it became abbreviated to "Hallowe'en" and then "Halloween."
Many centuries later, the Roman Catholic church, in an attempt to do away with pagan holidays, such as Halloween (and Christmas, which had been the Roman pagan holiday of Saturnalia) established November 1st as All Saint's Day (in French, la Toussaint), in celebration of all the saints who do not have their own holy day.
During the massive Irish immigration into America in the 1840s, Halloween found its way to the United States, where it continued to flourish!
One legend has it that on one All Hallows Eve that a priest was walking by on a country road when on the hill he saw the bonfires burning. He saw people dancing around the fire in costumes with shafts and torches in their hands. With the moon as a backdrop to the fires the people appeared to be flying in the air. The man hurried to the village to tell that witches were flying and evil was afoot. Presumably, this is where the myth of witches on broomsticks flying on Halloween comes from.
In the Celtic times and up till the medieval ages, fairies (a.k.a., faeries) were also thought to run free on the Eve of Samhain.Faeries weren't necessarily evil, but not particularly they weren't good. They were mischievous. They liked rewarding good deeds and did not like to be crossed. On Samhain, faeries were thought to disguise themselves as beggars and go door to door asking for handouts. Those who gave them food were rewarded. Those who did not were subjected to some unpleasantness.
In medieval times, one popular All Souls' Day practice was to make "soul cakes," simple bread desserts with a currant topping. In a custom called "souling," children would go door-to-door begging for the cakes, much like modern trick-or-treaters. For every cake a child collected, he or she would have to say a prayer for the dead relatives of the person who gave the cake. These prayers would help the relatives find their way out of purgatory and into heaven. The children even sang a soul cake song along the lines of the modern "Trick-or-treat, trick-or-treat, give me something good to eat."
Dressing up as ghouls and ghosts originated from the ancient Celtic tradition of townspeople disguising themselves as demons and spirits. The Celts believed that disguising themselves to look like the spirits who were wandering the earth that night might allow them to escape the notice of the real spirits wandering the streets.
If you are not from the British Isles, you won't believe where your hollowed out pumpkin comes from! In Ireland and Scotland hollowed-out turnips with embers or candles inside, became a very popular Halloween decoration a few hundred years ago. Tradition held that they would ward off Stingy Jack and other malevolent spirits on Halloween, and they also served as representations of the souls of the dead.Irish families who emigrated to America brought the tradition with them, but they replaced the turnips with pumpkins, which, native to the new world, were plentiful.It didn't hurt that they are a lot easier to carve than turnips.