Saint Mary Maggiore is a Major Papal Basilica, the largest Catholic Marian Church in Rome, and one of the Seven Pilgrim Churches of Rome. Santa Maria Maggiore, one of the first churches built in honour of the Virgin Mary, was erected in the immediate aftermath of the Council of Ephesus of 431, which proclaimed Mary Mother of God. The church retains the core of its original structure, despite several additional construction projects and damage by the earthquake of 1348. Church building in Rome in this period, as exemplified in Saint Mary Major, was inspired by the idea of Rome being not just the centre of the world of the Roman Empire, as it was seen in the classical period, but the centre of the Christian world. It is now agreed that the present church was built under Celestine I (422–432) not under Pope Sixtus III (432–440), who consecrated the basilica on the 5th of August 434 to the Virgin Mary. The dedicatory inscription on the triumphal arch, Sixtus Episcopus plebi Dei (Sixtus the bishop to the people of God), is an indication of that Pope’s role in the construction.
Pursuant to the Lateran Treaty of 1929 between the Holy See and Italy, the Basilica is within Italian territory and not the territory of the Vatican City State. However, the Holy See fully owns the Basilica, and Italy is legally obligated to recognize its full ownership thereof and to concede to it “the immunity granted by International Law to the headquarters of the diplomatic agents of foreign States.” In other words, the complex of buildings has a status somewhat similar to a foreign embassy.No Catholic church can be honoured with the title of basilica unless by apostolic grant or from immemorial custom. St. Mary Major is one of the only four that hold the title of major basilica. The other three are the basilicas of St. John in the Lateran, St. Peter, and St. Paul outside the Walls. (The title of major basilica was once used more widely, being attached, for instance, to the Basilica of St. Mary of the Angels in Assisi). Along with all of the other major basilicas, St. Mary Major is also styled a papal basilica. Before 2006, the four papal major basilicas, together with the Basilica of St. Lawrence outside the Walls were referred to as the patriarchal basilicas of Rome, and were associated with the five ancient patriarchates (see Pentarchy). St. Mary Major was associated with the Patriarchate of Antioch.
The five papal basilicas along with the Basilica of the Holy Cross in Jerusalem and San Sebastiano fuori le mura were the traditional Seven Pilgrim Churches of Rome, which were visited by pilgrims during their pilgrimage to Rome following a 20-kilometre (12 mi) itinerary established by St. Philip Neri on 25 February 1552.