The basilica was probably the first official christian cult place in Rome. According to the legend, it was ordered by Pope Callisto I during C.III and completed by the hand of San Giulio. It was the rebuilt under Innocenzo II and then underwent decorations and restoration, among which one especially remembers those promoted by Pope Clemente XI (1702) and Pope Pio IX (1870), without however having the church remarkably modified. Many parts of the church date back to C.XII; very important are the mosaics, especially the ones on the façades and in the apse, made by Pietro Cavallini and portraying the "Vita della Vergine". The bell-tower, built during C.XII, has a little mosaic portraying the Virgin on top. The porch was remodeled by Carlo Fontana in 1702. The balustrade has decorations of Popes’ statues. The basilical interior has three naves divided by twentyone granite columns, with diverse diameters, all bearing Ionian and Corinthian capitals. The very rich ceiling has carved and golden coffers with polychrome bottoms, on a drawing by Domenichino (1617) also painter of "L'Assunta".