Celts lived 2,000 years ago in the area that is now Ireland, the United Kingdom and Northern France. The people celebrated their new year November first. Celts believed that on the night before the new year, the boundary between the worlds of the living and the dead became blurred. On the night of October thirty-first they celebrated samhain(sow-in), when it was believed that the ghosts of the dead returned to earth.
In addition to causing trouble and damaging crops, druids built huge sacred bonfires, where people gathered to burn crops and animals as sacrifices to the celtics deities.During the celebration, Celts wore costumes, typically animal heads and skins, they even attempted to tell each others fortunes.
Halloween is also known as All Saints’ Day. On May 13, 609 A.D., Pope Boniface IV dedicated Pantheon in Rome in honor of all the Christian martyrs, and the catholic feast of all Martyrs Day was established in the Western church. Pope Gregory III later expanded the festival to include all saints as well as all martyrs, and moved the observance from May 13th to November 1st. The influence of Christianity had spread into Celtic lands, where it gradually blended with and supplanted the older Celtic rites.
Halloween is very different compared to the one they celebrated then and the one we celebrate now.