From the fourth century the Palace of the Lateran on Piazza San Giovanni in south-east Rome was the principal residence of the Popes, and continued so for about a thousand years.
The Domus Laterani 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 structure 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 basilica of the domus was converted and extended, eventually becoming the cathedral of Rome, the seat of the popes as patriarchs of Rome: see Basilica di San Giovanni in Laterano.
In the tenth Century Sergius III restored it after a disastrous fire, and later it was greatly embellished by Innocent III. This was the period of its greatest magnificence, when Dante speaks of it as beyond all human achievements. At this time the centre of the piazza in front, where now the obelisk stands, was occupied by the palace and tower of the Annibaldi family. Between this palace and the Lateran basilica was the equestrian statue of Marcus Aurelius, then believed to represent Constantine, which now is at the Campidoglio. The whole of the front of the palace was taken up with the Aula Concilii ("Hall of the Councils"), a magnificent hall with eleven apses, in which were held the various Councils of the Lateran during the medieval period. The private apartments of the popes in this palace were situated between this Triclinium and the city walls.
Two destructive fires, in 1307 and 1361 respectively, did irreparable harm, and although vast sums were sent from Avignon for the rebuilding, the palace never again attained its former splendour. When the popes returned to Rome they resided first at Basilica di Santa Maria in Trastevere, then at Basilica di Santa Maria Maggiore, and lastly fixed their residence at the Vatican. Sixtus V, more concerned with rationalized urban planning than the preservation of antiquities, then destroyed what still remained of the ancient palace of the Lateran in 1586 and erected the present much smaller edifice in its place.
From the old Lateran constructions three monuments survive, two of which are located in one building built by Domenico Fontana in 1589 opposite the Lateran Basilica. These monuments are the Scala Santa and the Chapel of the Sancta Sanctorum. Next to these is the third monument, the Triclinium of Leo III which survives as an apse lined with mosaics and open to the air. It was one of the most famous halls of the ancient palace, and was the state banqueting hall. The existing structure is not ancient, but it is possible that some portions of the original mosaics have been preserved in a three-part mosaic: In the centre Christ gives their mission to the Apostles, on the left he gives the keys to St. Sylvester and the Labarum to Constantine, while on the right St. Peter gives the stole to Leo III and the standard to Charlemagne.
Pope John XXIII returned to the palace some pastoral functions by fixing here the seat of the Vicariate and offices of the diocese of Rome.