Boo!

We owe the origin of Halloween to the Irish.

2000 years ago the ancient Celts celebrated the festival of Samhain (pronounced sow-in) in the area that is now Ireland, the United Kingdom and northern France.  November 1st marked the new year - the end of summer and the harvest and the beginning of the dark, cold winter this was the time time of year that was often associated with human death. The Celts believed that on the night before the new year, the boundary between the worlds of the living and the dead became blurred. 

In 609 A.D., Pope Boniface IV dedicated the Pantheon in Rome in honor of all Christian martyrs, and the Catholic feast of All Martyrs Day was established in the Western church. Pope Gregory III (731–741) later expanded the festival to include all saints as well as all martyrs, and moved the observance from May 13 to November 1. By the 9th century the influence of Christianity had spread into Celtic lands, where it gradually blended with and supplanted the older Celtic rites.