What does Halloween come from?

What does Halloween come from?
英文回答的,最多用四句话.

It takes some historical digging to come up with why we celebrate Halloween.
by Clark Humphrey
Most of America's big holidays have more-or-less self-explanatory purposes--to celebrate aspects of the Christian tradition,to honor the coming of the new year or the change of seasons,to remember the legacy of family members or noted historical figures.
But Halloween doesn't seem to fit in any of those above categories.
It takes some historical digging to come up with why we celebrate the eerie and the spooky on Oct.31.
One person who's done such a dig is Rosemary Ellen Guiley.According to Guiley,the origins of Halloween are a lot like the origins of Christmas and Easter as we practice them today--Ancient Roman,Catholic,and European Pagan lore,all blended together.
The name Halloween is Scottish in origin and is short for "All Hallow's Eve," the night before "All Hallow's Day," or All Saint's Day.That day was set by Pope Boniface IV to honor the Catholic saints,and also to replace a Roman pagan festival of the dead (which had been held in late February,the end of the old Roman year).Later,Pope Gregory III changed All Saint's Day to November 1.
By the time Christianity came to the British Isles,local folk had already been celebrating their own festival of the dead on Samhain (November 1,the Celtic new year).According to author Jack Santino in "Halloween and other Festivals of Death and Life" (University of Tennessee Press),"Many traditional beliefs and customs associated with Samhain,most notable that night was the time of the wandering dead,the practice of leaving offerings of food and drink to masked and costumed revelers,and the lighting of bonfires,continued to be practiced on 31 October."
In other words,the Christian church incorporated local Irish,Scottish,and Welsh pagan traditions into one of its own holy days.Just as the old fertility symbols of the rabbit and the evergreen tree became parts of Easter and Christmas,so have the symbols of the end of the fall harvest season and the coming of darkness become parts of a modern western-world celebration.