November 1 All Saints' Day
The origins of the holiday commemorating all the saints of the church are obscure, but by the mid-eighth century, November 1st was the day to honor all known and unknown saints in the Catholic Church.
In 837, its general observance was ordered by Pope Gregory IV The date may have been selected for its coincidence with pagan observations of the harvest, including the ancient Celtic festival of Samhain and the ancient Finnish celebration of Kekri.
Celtic festival of Samhain
Finnish celebration of Kekri