Feast of All Saints
All Saints' Day, also known as All Hallows' Day, the Feast of All Saints, the Feast of All Hallows, the Solemnity of All Saints, and Hallowmas, is a Christian solemnity celebrated in honour of all the saints of the church, whether they are known or unknown.

From the 4th century, feasts commemorating all Christian martyrs were held in various places, on various dates near Easter and Pentecost. In the 9th century, some churches in the British Isles began holding the commemoration of all saints on 1 November, and in the 9th century this was extended to the whole Catholic church by Pope Gregory IV.

In Western Christianity, it is still celebrated on 1 November by the Roman Catholic Church as well as many Protestant churches, as the Lutheran, Anglican, and Methodist traditions. The Eastern Orthodox Church and associated Eastern Catholic and Eastern Lutheran churches celebrate it on the first Sunday after Pentecost. The Church of the East and the Syro-Malabar Church and Chaldean Catholic Church, the latter of which is in communion with Rome, celebrates All Saints' Day on the first Friday after Easter Sunday. In the Coptic Orthodox tradition, All Saints' Day is on Nayrouz, celebrated on September 11. The day is both the start of the Coptic new year and its first month, Thout.
From the 4th century, there existed in certain places and at sporadic intervals a feast day to commemorate all Christian martyrs. It was held on 13 May in Edessa, the Sunday after Pentecost in Antioch, and the Friday after Easter by the Syrians. During the 5th century, St. Maximus of Turin preached annually on the Sunday after Pentecost in honor of all martyrs in what is today northern Italy. The Comes of Würzburg, the earliest existing ecclesiastical reading list, dating to the late 6th or early 7th century in what is today Germany, lists this the Sunday after Pentecost as dominica in natale sanctorum ("Sunday of the Nativity of the Saints"). By this time, the commemoration had expanded to include all saints, martyred or not.

On 13 May 609 or 610, Pope Boniface IV consecrated the Pantheon at Rome to the Blessed Virgin Mary and all the martyrs, ordering an anniversary; the feast of dedicatio Sanctae Mariae ad Martyres has been celebrated at Rome ever since. It is suggested 13 May was chosen by the Pope and earlier by Christians in Edessa because it was the date of the Roman pagan festival of Lemuria, in which malevolent and restless spirits of the dead were propitiated. Some liturgiologists base the idea that Lemuria was the origin of All Saints on their identical dates and their similar theme of "all the dead".[a]

Pope Gregory III (731–741) dedicated an oratory in Old St. Peter's Basilica to 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". Some sources say Gregory III dedicated the oratory on 1 November, and this is why the date became All Saints' Day. Other sources say Gregory III held a synod to condemn iconoclasm on 1 November 731, but dedicated the All Saints oratory on Palm Sunday, 12 April 732.

By 800, there is evidence that churches in Ireland, Northumbria (England) and Bavaria (Germany) were holding a feast commemorating all saints on 1 November. Some manuscripts of the Irish Martyrology of Tallaght and Martyrology of Óengus, which date to this time, have a commemoration of all saints of the world on 1 November. In the late 790s, Alcuin of Northumbria recommended holding the feast on 1 November to his friend, Arno of Salzburg in Bavaria. Alcuin then used his influence with Charlemagne to introduce the Irish-Northumbrian Feast of All Saints to the Frankish Kingdom.

Some scholars propose that churches in the British Isles began celebrating All Saints on 1 November in the 8th century to coincide with or replace the Celtic festival known in Ireland and Scotland as Samhain. James Frazer represents this school of thought by arguing that 1 November was chosen because Samhain was the date of the Celtic festival of the dead. Ronald Hutton argues instead that the earliest documentary sources indicate Samhain was a harvest festival with no particular ritual connections to the dead. Hutton proposes that 1 November was a Germanic rather than a Celtic idea.

The 1 November All Saints Day was made a day of obligation throughout the Frankish Empire in 835, by a decree of Emperor Louis the Pious, issued "at the instance of Pope Gregory IV and with the assent of all the bishops", which confirmed its celebration on 1 November. Under the rule of Charlemagne and his successors, the Frankish Empire developed into the Holy Roman Empire.

Sicard of Cremona, a scholar who lived in the 12th and 13th centuries, proposed that Pope Gregory VII (1073–85) suppressed the feast of 13 May in favour of 1 November. By the 12th century, 13 May had been deleted from liturgical books.

The All Saints octave was added by Pope Sixtus IV (1471–84). Both the All Saints vigil and the octave were suppressed by the Liturgical reforms of Pope Pius XII in 1955.
1 November (Western Christianity)
Sunday after Pentecost (Eastern Christianity)