The first two days in November in a Catholic church dedicated to the memory of the dead: November 1 All Saints 'Day (All Saints' Day) and November 2 All Souls 'Day (All Souls' Day) one after the other.
Halloween has deep pagan roots. About two thousand years ago, the Celtic tribes at this time were celebrating the Lunar New Year, which was celebrated on the eve of the festival of Samhain (Samhain). This is borderline time (the transition to winter) time was considered magical and mystical — seeds (neutral, and often hostile to humans magical creatures) come to the human world, but people also have the opportunity to go to the next world.
It was also believed that the souls of the dead on this day returned to their homes and require sacrificial food in living. At about the same time (late October), the ancient Romans celebrated two holidays — Feralii dedicated to the memory of the dead, and the days of Pomona, the goddess of fruit of the trees.
The coincidence of dates helped to preserve the tradition of remembrance of the dead and after the widespread the spread of Christianity. The holiday has grown together in the popular mind with the holiday church. So there was All Saints Day, which is still celebrated by the Catholic Church on November 1. All hallow ees (Mass in All Saints) — that was his distorted view of Old English name, so that the "Halloween" — is nothing more than "Eve Ollholuisa».
In this case, pagan ideas leecher in the medieval Christian mind become a representation of evil spirits coming out on that day to scare the pious inhabitants. That is why in the Middle Ages and modern times Halloween witch chosen, be sure to arrange this day Sabbath.
Feast of All Saints was originally celebrated May 13, on this day in 609, Pope Boniface IV consecrated the Roman rotunda dedicated to the Virgin Mary and all the great martyrs of the church (according to other sources this festival has introduced Pope Gregory IV in 835 year). And in the early 11th century, this holiday was moved to November 1 (if this day was dedicated to those saints who did not have their holiday during the year).