In the first century A.D., the Romans brought along a couple of their own festivals to add to Samhain. Poloma, the goddess of fruit was honored, and the Festival of Feralia was to honor the dead.
The Christians came along around the eighth century A.D., and declared November 1 as All Saints Day, to honor those saints who had no designated day of their own. The mass held on All Saints Day was called Allhallowmas or the Mass of All Hallows, with hallows meaning saints. Thus, the night before the mass was called All Hallows Eve, which eventually was shortened to Halloween.