Halloween originated over 2000 years ago in Ancient Britain and Ireland. The Celtic peoples celebrated Samhain near the end of October to mark the end of the harvest and the beginning of the new year.The Gateway: From Pagans to Catholics: The Origins of Halloween
Ancient Celtic Roots
Samhain (pronounced Sow-in) was the festival celebrated at the end of the harvest on October 31, which was the last day of the Celtic year. This day also marked the beginning of winter for the Celts, who associated winter with death, and believed that the limits, or veil between the living and the dead were very thin on this night.http://www.history.com/content/halloween/real-story-of-halloween
Because they believed the veil between worlds was so thin on Halloween night, the Celts thought that spirits were able to cross over from the otherworld. These spirits were believed to strengthen one's ability to divine the future. Thus people walked around in costumes made from animal skins, divining each other's futures.http://www.history.com/minisite.do?content_type=Minisite_Generic&content_type_id=713&display_order=1&sub_display_order=1&mini_id=1076
It was seen as necessary to offer sacrifices and appease the spirits, in order to turn their wrath and attention elsewhere. This was a time of fear for the Celts and it was taken very seriously.http://www.youtube.com/watch?v=fPF4nJYoHxw
Origins Of Halloween
This video gives a brief history of the Celtic relationship with Halloween, then goes on to reveal the Catholic Church's role. The narrator compares the festivals of the dead and various celebrations and customs of a number of different cultures around the world, and shows the similarities.
Celtic Origins of Halloween in Ireland
This video attributes the origins of Halloween to the Celts of Ireland. Winter is described as a scary time, when mortality was thought about more. Samhain represented the transition between Summer and Winter and they believed things could occur on that night that could not any other night of the year.