The origin of All Saints’ Day cannot be traced with certainty, and it has been observed on various days in different places.
All Saints Day is a surprisingly old feast. It arose out of the Christian tradition of celebrating the martyrdom of saints on the anniversary of their martyrdom. When martyrdoms increased during the persecutions of the late Roman Empire, local dioceses instituted a common feast day in order to ensure that all martyrs, known and unknown, were properly honored.
The current date of November 1 was instituted by Pope Gregory III (731-741) when he consecrated a chapel to all the martyrs in Saint Peter’s Basilica in Rome. Gregory ordered his priests to celebrate the Feast of All Saints annually. This celebration was originally confined to the diocese of Rome, but Pope Gregory IV (827-844) extended the feast to the entire Church and ordered it to be celebrated on November 1.