In August of 356, the Virgin appeared in a dream before Pope Liberius and commanded him to build a church on the site where it would snow the following day. (It does NOT snow in Rome!)
The Basilica was built in the time of Pope Sixtus III (432 - 440). The Romanesque campanile (bell tower) is the tallest in Rome.
The Basilica, showing the campanile and the base of the Corithian Column
The Corithian Column in front of the Basilica. It was erected by Pope Paul V who had it brought from the Basilica of Maxentius in the Roman Forum in 1615.
Looking down the main isle towards the altar. The ceiling, by Guiliano Sangallo, was gilded with the first gold bought from the Americas.
A closer view of the altar, showing the canopy (baldacchino) designed by Fuga (who also designed the facade) and supported on four porphyry columns. The canopy is of 18th century construction.
The apse mosaic, by Jacopo Torriti, from 1295. There's also a page with close up views of the apse.
On the main altar there is a sarcophagus containing the bones of St. Matthew the Evangelist. Beneath the altar is a statue of Pope Pius IX by Jacometti (1880), back to camera here. And underneath the altar behind the metal grill are the celebrated relics of the crib, which legend says consists of five pieces of the manager in which Christ was put at birth.
The Pauline Chapel, with an altar to the Virgin by P. Targoni (1600). This chapel was built by the architect Flaminio Ponzio, and contains the tomb of Pope Paul V (1605 - 1624) and Clement VIII Aldobrandini (1592 - 1605).