The Lateran Palace, sometimes more formally known as the Palace of the Lateran, is an ancient palace of the Roman Empire and later a Palace of the Popes. Adjacent to the Basilica di San Giovanni in Laterano, the cathedral church of Rome, Italy, the Lateran Palace is now home of the Pontifical Museum of Christian Antiquities.
From the beginning of the 4th Century, when it was given to the Pope by Constantine, 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.
In the 10th 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 Annibaldeschi. Between this palace and the Lateran Basilica was the equestrian statue of Marcus Aurelius, then believed to represent Constantine, which now is at the Capitol. The whole of the front of the palace was taken up with the "Aula Concilii", a magnificent hall with eleven apses, in which were held the various Councils of the Lateran during the medieval period. The private rooms 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 Santa Maria in Trastevere, then at Basilica di Santa Maria Maggiore, and lastly fixed their residence at the Vatican. Sixtus V then destroyed what still remained of the ancient palace of the Lateran and erected the present much smaller edifice in its place.
An apse lined with mosaics and open to the air still preserves the memory of one of the most famous halls of the ancient palace, the "Triclinium" of Leo III, which 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.