HALLOWEEN
All Hallows' Eve, or Halloween is a holiday celebrated each year on October 31.
In the eighth century, Pope Gregory III designated November 1 as a time to honor all saints. Soon, All Saints Day incorporated some of the traditions of Samhain. The evening before was known as All Hallows Eve, and later Halloween. Over time, Halloween evolved into a day of activities like trick-or-treating, carving jack-o-lanterns, festive gatherings, donning costumes and eating treats.
The word itself literally means "hallowed evening," and was previously known to early European celebrators as All Hallows' Eve. All Hallows' Eve (October 31) and All Saints' Day (November 1) both paid homage to saints ("hallows" = saints). The name was eventually shortened to "Halloween," which we know and love to this day.
The tradition originated with the Celtics who lived 2,000 years ago.
The Celts, mostly in the area that is now Ireland, the United Kingdom and northern France, celebrated their new year on November 1. October 31 marked the end of summer and the harvest and the beginning of the dark, cold winter, a time of year that was often associated with human death. 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 31 they celebrated Samhain, when it was believed that the ghosts of the dead returned to earth.
During the Samhain festival the souls of those who had died were believed to return to visit their homes, and those who had died during the year were believed to journey to the otherworld. People set bonfires on hilltops for relighting their hearth fires for the winter and to frighten away evil spirits, and they sometimes wore masks and other disguises to avoid being recognized by the ghosts thought to be present. It was in those ways that beings such as witches, hobgoblins, fairies, and demons came to be associated with the day. The period was also thought to be favourable for divination on matters such as marriage, health, and death. When the Romans conquered the Celts in the 1st century CE, they added their own festivals of Feralia, commemorating the passing of the dead, and of Pomona, the goddess of the harvest.
https://www.history.com/topics/halloween/history-of-halloween