Some do not recognize Halloween has a history dating back about 2000 years ago. The holiday was first associated with the Celtic festival of Samhain; a festival of light verses dark, how summer has ended and winter has begun. It also marked the end of the year, an equivalent to New Years Eve. On this night, October 31, saints were allowed to pass through the division of the world allowing family members and friends to enjoy the presence of their departed loved ones.
To protect themselves during the time of transition for spirits, people would wear masks for disguise to protect themselves if the harmful spirits passing through were vengeful in their desires. Believers would allow Druids, or Celtic Priests, to make predictions of their future. This would provide comfort for those expecting the worst of the year to come, and have their fears of the harmful spirits silenced.
One would find houses darkened as very large bonfires were lit on hills and fields. Families would eventually light the small fires within the household after the festival to commemorate the start of the new year. The population would celebrate this festival with a very large bonfire on the Mound of Hostages, the mound dating back to 4,500 years ago. Food played a large part in the celebration of familial spirits, as livestock were slaughtered and meals were prepared for the living and the dead. This was one of the most crucial pre-Christian Irish.
As years went on, the holiday soon combined All Saints Day designated by Pope Gregory the Third around 735 A.D. The holiday honored the saints and Christian martyrs on November 1st, and slowly integrated itself into the traditions of Samhain. In an attempt to provide more church related holidays, All Souls day was established. It was the celebration of the dead taking place on November 2nd, the day after All Saints Day. Parades, bonfires, festivities, would all take place, very similar to Samhain. During parades, the poor would beg hoping to receive some of the extra food from the festival. Those who were well-off would hand the beggars Soul Cakes, pastries, and in return make them promise to pray for the families departed loved ones. It was encouraged by the church, as people were taking care of those who are less blessed than them. It was called “going-a-souling” and, soon, one could find children begging on doorsteps for sweets. This created the tradition of Trick or Treating. The holiday was also known as All-Hallows Eve and has turned into, as we are now familiar with, Halloween.
Source: history.com