The basilica of Santa Maria in Trastevere is one of the oldest churches in Rome, perhaps the first in which mass was openly celebrated. It stands in Trastevere rione. It is believed to be the first church in Rome to be dedicated to the Blessed Virgin Mary, at its rebuilding in the 12th century.
The predecessor of the present church was probably built in the early fourth century although that church was the successor to one of the tituli, those Early Christian basilicas that were ascribed to a patron and perhaps literally inscribed with his name. Though nothing remains to establish with certainty where any of the public Christian edifices of Rome before the time of Constantine the Great were situated, the basilica on this site was known as Titulus Callisti, since a legend in the Liber Pontificalis ascribed the earliest church here to a foundation by Pope Callixtus I (died 222), whose remains, translated to the new structure, are preserved under the altar.
The present nave of this Romanesque church, rebuilt by Pope Innocent II (1138 –1148) and rededicated to the Virgin Mary, preserves its original basilica plan and stands on the earlier foundations. The 22 granite columns with Ionic capitals that separate the nave from the aisles came from the ruins of an ancient Roman building, as did the lintel of the entrance door.
Inside the church are a number of late 13th-century mosaics by Pietro Cavallini on the subject of the Life of the Virgin (1291) centering on a "Corontation of the Virgin" in the apse. Domenichino's octagonal ceiling painting, Assumption of the Virgin (1617) fits in the coffered ceiling setting he designed.
The façade of the church was restored by Carlo Fontana in 1702, who replaced the ancient porch with a sloping tiled roof— seen in Falda's view (upper right)— with the present classicizing one (below right). The octagonal fountain in the piazza in front of the church (Piazza di Santa Maria in Trastevere), which already appears in a map of 1472 [1], was also restored by Carlo Fontana.
The church keeps a relic of Saint Apollonia, her head, as well as a portion of the Holy Sponge. Among those buried in the church, are the relics of Pope Callixtus I and the body of Lorenzo Cardinal Campeggio.

This is but one of the ancient churches in Trastevere. Christianity penetrated this part of Rome early on because here, in imperial times, there was less control by the authorities and because many foreigners resided in the area. The church was probably built in the 3rd century AD where the young noble martyr Cecilia used to live.
You can visit excavations from the right-hand nave and see the ruins of a colonnaded building of the 2nd century AD. Above these, there are chambers that lead into a hall with 7 brick vats used for tanning skins and hides, a testament to the fact that Trastevere was once a business and mercantile center. The church was completely rebuilt in the 9th century, during the pontificate of Pascal I, but it underwent a great number of other changes before the 17th century.
The beautiful 12th century cloister was altered by a wall built in the 16th century to hold up the nuns' refectory built above. It is here in the nuns' quarters that you can see one of the greatest paintings from the Middle Ages: the Last Judgement, painted in 1293 by Pietro Cavallini on the wall of the counter-façade. The fresco was later hidden by the choir which was constructed to allow the enclosed order of nuns to take part in religious services.
In this grandiose fresco, Cavallini's strong artistic personality shines through. He knew how to apply color so that, within the monumental design of the whole work, the figures come alive and stand out. Recent studies have concluded that this master of the Roman school was the greatest innovator of Italian painting at the end of the Middle Ages.