The Papal Archbasilica of St. John Lateran (Italian: Arcibasilica Papale di San Giovanni in Laterano) is the cathedral of the Church of Rome, Italy, and the official ecclesiastical seat of the Bishop of Rome, who is the Pope. Officially named Archibasilica Sanctissimi Salvatoris et Sancti Iohannes Baptista et Evangelista in Laterano (English: Archbasilica of the Most Holy Saviour and Sts. John the Baptist and the Evangelist at the Lateran", Italian: Arcibasilica del Santissimo Salvatore e Santi Giovanni Battista ed Evangelista in Laterano), it is the oldest and ranks first among the four Papal Basilicas or major basilicas of Rome (having the cathedra of the Bishop of Rome).  It claims the title of ecumenical mother church (mother church of the whole inhabited world) among Roman Catholics. The current archpriest of St. John Lateran is Agostino Vallini, Cardinal Vicar General for the Diocese of Rome. The President of the French Republic, currently Nicolas Sarkozy, is ex officio the "first and only honorary canon" of the basilica, a title inherited from the Kings of France, who have held it since Henry IV.

An inscription on the façade, Christo Salvatori, indicates the church's dedication to the "Christ the Saviour", for the cathedrals of all patriarchs are dedicated to Christ Himself. As the cathedral of the Bishop of Rome, containing the papal throne (Cathedra Romana), it ranks above all other churches in the Roman Catholic Church, including St. Peter's Basilica in the Vatican.

The cathedral itself is located outside of the Vatican City boundaries, territorially located within the city of Rome in the Italian Republic. However it has been granted a special extraterritorial status as a property of the Holy See. This is also the case with several other buildings after the solving of the Roman Question with the Lateran Treaty.

Lateran Palace

The basilica itself stands over the remains of the Castra Nova equitum singularium, the 'new fort' of the imperial cavalry bodyguard. The fort had been established by Septimius Severus in AD 193, but following the victory over Maxentius (whom the Equites singulares augusti had fought for) at the Battle of the Milvian Bridge by Constantine I the guard were abolished and the fort demolished. Substantial remains of the fort lie directly beneath the basilica nave. The rest of the Basilica site was occupied during the early Roman Empire by the palace of the gens Laterani. The Laterani served as administrators for several emperors; Sextius Lateranus was the first plebeian to attain the rank of consul. One of the Laterani, Consul-designate Plautius Lateranus, became famous for being accused by Nero of conspiracy against the emperor. The accusation resulted in the confiscation and redistribution of his properties.

The Lateran Palace fell into the hands of the emperor when Constantine I married his second wife Fausta, sister of Maxentius. Known by that time as the "Domus Faustae" or "House of Fausta," the Lateran Palace was eventually given to the Bishop of Rome by Constantine. The actual date of the gift is unknown but scholars believe it had to have been during the pontificate of Pope Miltiades, in time to host a synod of bishops in 313 that was convened to challenge the Donatist schism, declaring Donatism as heresy. The palace basilica was converted and extended, becoming the residence of Pope St. Silvester I, eventually becoming the cathedral of Rome, the seat of the popes as bishops of Rome.

The Middle Ages

The basilica's claim to being the head church in the world.

The official dedication of the Basilica and the adjacent Lateran Palace was presided over by Pope Sylvester I in 324, declaring both to be Domus Dei or "House of God." In its interior, the Papal Throne was placed, making it the Cathedral of the Bishop of Rome. In reflection of the basilica's claim to primacy in the world as "mother church", the words Sacrosancta Lateranensis ecclesia omnium urbis et orbis ecclesiarum mater et caput (meaning "Most Holy Lateran Church, of all the churches in the city and the world, the mother and head") are incised in the front wall between the main entrance doors.

The Lateran Palace and basilica have been rededicated twice. Pope Sergius III dedicated them to Saint John the Baptist in the 10th century in honor of the newly consecrated baptistry of the Basilica. Pope Lucius II dedicated the Lateran Palace and basilica to Saint John the Evangelist in the 12th century. However, St. John Baptist and St. John the Evangelist are regarded as co-patrons of the Cathedral, the chief patron being Christ the Saviour himself, as the inscription in the entrance of the Basilica indicates, and as is tradition in the patriarchal cathedrals. Thus, the Basilica remains dedicated to the Saviour, and its titular feast is the Transfiguration. That is why sometimes the Basilica will be referred to by the full title of Archbasilica of the Most Holy Saviour and of Sts. John Baptist and John Evangelist in the Lateran. The church became the most important shrine in honor of the two saints, not often jointly venerated  In later years, a Benedictine monastery was established at the Lateran Palace, devoted to serving the basilica as a devotional to the two saints.

Every pope from Miltiades occupied the Lateran Palace until the reign of the French Pope Clement V, who in 1309 decided to transfer the official seat of the Catholic Church to Avignon, a papal fief that was an enclave within France. The Lateran Palace has also been the site of five Ecumenical councils. See Lateran councils.

During the Avignon papacy, the Lateran Palace and the basilica began to decline. Two destructive fires ravaged the Lateran Palace and the basilica, in 1307 and again in 1361. In both cases, the Avignon papacy sent money to their bishops in Rome to cover the costs of reconstruction and maintenance. Despite the action, the Lateran Palace and the basilica lost their former splendor.

When the Avignon papacy formally ended and the Bishop of Rome again resided in Rome, the Lateran Palace and the basilica were deemed inadequate considering the accumulated damage. The popes took up residency at the Basilica di Santa Maria in Trastevere and later at the Basilica di Santa Maria Maggiore. Eventually, the Palace of the Vatican was built (adjacent to the Basilica of St. Peter, that already existed at the Vatican since the time of Constantine), and the papacy moved in; the papacy remains there today.

Reconstruction

There were several attempts at reconstruction of the basilica before Pope Sixtus V's definitive project. Sixtus hired his favorite architect Domenico Fontana to oversee much of the project. The original Lateran Palace was torn down and replaced with a new building. On the square in front of the Lateran Palace is the largest standing obelisk in the world, known as the Lateran Obelisk (weight estimated at 455 tons). Its manufacture was started by Thutmose III and it was erected by Thutmose IV before the great Karnak temple of Thebes, Egypt.  Intended by Constantine I to be shipped to Constantinople, the very pre-occupied Constantius II had it shipped instead to Rome, where it was re-erected in the Circus Maximus in 357. At some time it broke and was buried under the Circus. In the 16th century it was located and dug up, and Sixtus V had it re-erected on a new pedestal on August 3, 1588 on its present site.

Further renovation on the interior of the basilica ensued under the direction of Francesco Borromini, commissioned by Pope Innocent X. The twelve niches created by his architecture came to be filled by 1718 with statues of the apostles, using the most prominent Roman Rococo sculptors.

The vision of Pope Clement XII for reconstruction was an ambitious one: he launched a competition to design a new façade. Over 23 architects, mostly working in the current Baroque idiom competed. The putatively impartial jury was chaired by Sebastiano Conca, president of the Roman Academy of Saint Luke. The winner of the competition was Alessandro Galilei. The façade as it appears today was completed in 1735. Galilei's façade however removed all vestiges of traditional ancient basilica architecture, and imparted a neo-classical facade.