The origins go back to a Celtic holiday called Samhain which marked the start of winter and the end of the harvest, which included the slaughtering of animals for winter food.
The belief was that the coming darkness of winter meant that spirits of the dead could cross over to the world of the living to visit or haunt them.
In the Middle Ages, the Christian church took many pagan holidays and adopted and adapted them to their own purposes to bring pagans into the faith. The day after Halloween became known as All Saints’ or All Hallows’ Day meant to honor Christian saints and martyrs. In the church's version, the dead saints could intercede in a good way in the affairs of the living.
In those earlier days, churches held masses for the dead and put bones of the saints on display on All Saints Day, and the night before was All Hallows’ Eve (not Halloween) and people baked "soul cakes" lit bonfires and set out lanterns carved out of turnips to keep the ghosts of the dead away.
by Henry Wadsworth Longfellow
All houses wherein men have lived and died
Are haunted houses. Through the open doors
The harmless phantoms on their errands glide,
With feet that make no sound upon the floors.
We meet them at the door-way, on the stair,
Along the passages they come and go,
Impalpable impressions on the air,
A sense of something moving to and fro.
There are more guests at table than the hosts
Invited; the illuminated hall
Is thronged with quiet, inoffensive ghosts,
As silent as the pictures on the wall.
The stranger at my fireside cannot see
The forms I see, nor hear the sounds I hear;
He but perceives what is; while unto me
All that has been is visible and clear.
So from the world of spirits there descends
A bridge of light, connecting it with this,
O’er whose unsteady floor, that sways and bends,
Wander our thoughts above the dark abyss.
excerpted from “Haunted Houses” by Henry Wadsworth Longfellow. Public domain.
Visit our website at poetsonline.org