All Saints is a Roman Catholic holiday on November 1, followed by All Souls Day on November 2. The Eastern Orthodox Church's All Saints is the first Sunday after Pentecost.
The festival of All Saints (Festum omnium sanctorum), also formerly known as "All Hallows," or "Hallowmas," is a feast celebrated in honour of all the saints and martyrs, known or unknown. In the Roman Catholic Church it is a festival of the first rank, with a vigil and an octave.
Common commemorations, by several churches, of the deaths of martyrs began to be celebrated in the 4th century. The first trace of a general celebration is in Antioch on the Sunday after Pentecost. This custom is also referred to in the 74th homily of John Chrysostom (407) and is maintained to the present day in the Eastern Ortodox Church.
The origin of the festival of All Saints as celebrated in the West is, however, now said to be somewhat doubtful. On May 13 in 609 or 610 (the day being more important than the year), Pope Boniface IV consecrated the Pantheon at Rome to the Blessed Virgin and all the martyrs, and the feast of the dedicatio Sanctae Mariae ad Martyres has been celebrated at Rome ever since. The day, May 13, was a pagan observation of great antiquity, the culmination of three days of the Feast of the Lemures, in which were propitiated the malevolent and restless spirits of all the dead. The idea, based on the medieval liturgiologists, that this festival was the origin of that of All Saints has now been abandoned by Roman Catholics. The latter is possibly traceable to the foundation by Pope Gregory III (731-741) of an oratory in St Peter's for the relics "of the holy apostles and of all saints, martyrs and confessors, of all the just made perfect who are at rest throughout the world", with the day moved to November 1.
So far as the Western Church generally is concerned, the festival was already widely celebrated in the days of Charlemagne and was made a day of obligation throughout the Frankish empire in 835, by a decree of Louis the Pious, issued "at the instance of Pope Gregory IV and with the assent of all the bishops," which confirmed its celebration on the 1st of November.
The festival was retained at the Reformation in the calendar of the Church of England, and also in that of many of the Lutheran churches. In the latter, in spite of attempts at revival, it has fallen into disuse. In the Lutheran churches, such as the Church of Sweden, it assumes a role of commemoration of the dead. In the Swedish calendar observance takes place on the first Saturday of November.