Major basilica (Latin: Basilica maior; plural: Basilicae maiores) is the title given to the four highest-ranking Roman Catholic church buildings, all of which are also "Papal basilicas": the Archbasilica of St. John Lateran, St. Peter's Basilica, the Basilica of St. Paul Outside the Walls, and the Basilica di Santa Maria Maggiore. All of them are located within the diocese of Rome: St. Peter's Basilica is located in Vatican City and thus within the territory and sovereign jurisdiction of the Holy See, while the other three are located in Italian territory. The Archbasilica of St. John in the Lateran is the seat of the Pope and the site of the Papal Cathedra, and is the oldest and first in rank of the Major Basilicas.
All other churches that have the title of basilica are minor basilicas (Latin: basilica minor).
Major basilica Wikipedia
The title of "major basilica" was introduced in 1300 by Pope Boniface VIII. With the promulgation of the bull Antiquorum fida relatio, he instituted the Holy Year and set the conditions for its indulgences. Boniface VIII renewed certain "great remissions and indulgences for sins" which were to be obtained "by visiting the city of Rome and the venerable basilica of the Prince of the Apostles". He offered "not only full and copious, but the most full, pardon of all their sins" to those who fulfilled certain conditions: First, as truly penitent, they had to confess their sins, and, second, they had to visit on pilgrimage the Basilicas of St. Peter and St. Paul, the respective burial sites of the Apostles Pope St. Peter and St. Paul.
In the second jubilee year in 1350, Pope Clement VI designated as a third major basilica St. John in the Lateran, the Cathedral of Rome. He encouraged the faithful to make daily visits to St. John in the Lateran, besides those to the Basilicas of St. Peter and St. Paul. Finally, for the next jubilee year in 1390, the Basilica of St. Mary Major, the oldest church in Rome dedicated to the Blessed Virgin, was added to the list. Visiting these four churches has remained one of the conditions for gaining the Roman Jubilee indulgence.
Pursuant to the Lateran Treaty of 1929 between the Vatican City State and Italy, the three Major Basilicas located in Rome, but not within the territory of the Vatican City itself (as is the Major Basilica of St. Peter's), are within Italian territory and not the territory of the Vatican City State. However, the Holy See fully owns these three Major Basilicas not within the territory of the Vatican City, and Italy is legally obligated to recognize its full ownership thereof and to concede to these three properties "the immunity granted by International Law to the headquarters of the diplomatic agents of foreign States". Thus, while of the Major Basilicas, the Basilica of St. Peter's alone is within the territory and sovereign jurisdiction of the Vatican City, the other three major basilicas enjoy extraterritorial status similar to that of foreign embassies while being within Italian Territory. Consequently, all four of the Major Basilicas are patrolled internally by police agents of Vatican City State. These properties, located across Rome, are legally deemed to be essential institutions necessary to the character and mission of the Holy See for which extraterritoriality is justified.
The four Major Basilicas, together with the Minor Basilica of Saint Lawrence outside the Walls, all of which are in Rome, were formerly known as "patriarchal basilicas", along with a few other churches outside of Rome. Upon relinquishing the title of "Patriarch of the West" in 2006, Pope Benedict XVI officially renamed the "patriarchal basilicas" as "Papal basilicas". The five, formerly styled "patriarchal basilicas" of Rome were previously assigned to and associated with the five ancient patriarchates of the Latin Church, or the Pentarchy:St. John Lateran was associated with Rome (Patriarch of the West),
St. Peter's with Constantinople (Latin Patriarch of Constantinople),
St. Paul's with Alexandria (Latin Patriarch of Alexandria),
St. Mary Major with Antioch (Latin Patriarch of Antioch), and
St. Lawrence with Jerusalem (Latin Patriarch of Jerusalem).
As indicated, the title of "patriarchal basilica", now replaced with "Papal basilica", was also officially given to two churches associated with St. Francis of Assisi and situated in or near his home town of Assisi, Italy:Papal Basilica of St. Francis of Assisi
Papal Basilica of St. Mary of the Angels
Thus there are four Papal Major Basilicas and three Papal Minor Basilicas. In addition, there is a multitude of minor basilicas throughout the world which have not been granted the official appellation "Papal" as the aforementioned three have.
To this class belong the four great ancient churches of Rome:Archbasilica of St. John Lateran, also called the Lateran Archbasilica, is the cathedral of the Bishop of Rome, the Pope. It is the only one called an "archbasilica". Its full official name is "Papal Archbasilica of the Most Holy Saviour and of Saints John the Baptist and the Evangelist at the Lateran, Cathedral of Rome".
St. Peter's Basilica, also called the Vatican Basilica, is a major pilgrimage site, built over the burial place of Saint Peter. Perhaps the largest church in the world, it is used for most of the chief religious ceremonies in which the Pope participates. Its official name is the "Papal Basilica of Saint Peter in the Vatican".
Basilica of Saint Paul Outside the Walls, also known as the Ostian Basilica because it is situated on the road that led to Ostia, is built over the burial place of Paul the Apostle. Its official name is the "Papal Basilica of Saint Paul Outside the Walls".
Basilica di Santa Maria Maggiore, also called the Liberian Basilica because the original building (not the present one) was attributed to Pope Liberius, is the largest church in Rome dedicated to the Blessed Virgin Mary, hence its name of Saint Mary Major, i.e. the Greater. Its official name is the "Papal Basilica of Saint Mary Major".
These four major basilicas are distinguished by their having a holy door and for being prescribed as destinations for visits as one of the conditions for gaining the Roman Jubilee. Only the Pope and his delegatees may celebrate mass at the high altar. Until recently, the four churches were open 24 hours a day; their staff included a college of priests to be continually available to hear confessions.