The first two days of November in the Catholic Church are dedicated to the memory of the deceased: November 1, All Saints' Day and November 2, All Souls' Day follow one after another.
The Christian holiday All Saints' Day has deep pagan roots. About two thousand years ago, Celtic tribes at this time celebrated the New Year, on the eve of which the Samhain holiday was celebrated. This borderline time (the transition to winter) was considered a magical and mystical time — seeds (neutral and often hostile magical creatures to people) come into the world of people, and people also have the opportunity to «visit» in the other world.
It was also believed that the souls of the dead returned to their homes on this day and demanded sacrificial food from the living. Around the same time (at the end of October), the ancient Romans celebrated two festivals of — Feralia, dedicated to the memory of the dead, and the days of Pomona, the goddess of tree fruits.
This coincidence of dates contributed to the preservation of the tradition of commemorating the dead even after the widespread spread of Christianity. The holiday has grown together in the popular consciousness with the church holiday. This is how All Saints' Day appeared, which is still celebrated by the Catholic Church on November 1st. All hallow ees (Mass of All Saints) — was its distorted Old English name, so «Halloween» — is nothing more than «Allholuis' Eve».
At the same time, pagan ideas about the Sids in the medieval Christian consciousness turned into ideas about the evil spirits coming out on this day to frighten the pious inhabitants. That is why in the Middle Ages and Modern Times, Halloween was chosen by witches who always organized a Sabbath on this day.
The Feast of All Saints was originally celebrated on May 13, on this day in 609 Pope Boniface IV consecrated the Roman rotunda dedicated to Our Lady and all the great martyrs of the church (according to other sources, this holiday was introduced by Pope Gregory IV in 835). And at the beginning of the 11th century, this holiday was moved to November 1 (then this day was dedicated to those saints who did not have their own holiday for a year). In a number of countries it is a day off and a national holiday.