Mausoleum of Santa Costanza site features

The Mausoleum of Santa Costanza is a squat circular brick drum standing in open ground beside the basilica of Sant’Agnese, low and plain outside, with a shallow conical roof and a ring of small arched windows near the top. From the path it looks closed and unremarkable.

Inside it opens into two rings. You enter through a narthex with two apses at the sides into a circular corridor covered by a barrel vault, which runs all the way round a central space — two concentric circular spaces, one dark and enclosing, the other bright and open.

Twelve pairs of columns separate them. Granite shafts taken from an earlier building of the Roman period stand in couples, carrying arches, so the centre is seen through a screen of columns from everywhere in the ambulatory.

The light falls from above, in the middle. A dome of 22.50 m in diameter rises over the central space, lit by twelve arched windows; the dome itself is bare, because its mosaics were removed by Urban VIII. The ambulatory, by contrast, is low-vaulted and dim.

And that dim vault is covered in colour. The 4th-century mosaics run the whole circuit overhead on a white ground: geometric motifs, then panels of fruit, flowers, peacocks and doves, then grape-harvest scenes — vine tendrils, figures treading grapes, carts — in green, gold, red and dark blue, which is why the building was taken for a temple of Bacchus.

The walls carry niches, and one holds a tomb. Rectangular and semicircular niches punctuate the outer wall; in the end niche stands a copy of Costanza's red porphyry sarcophagus, deep purple-red and massive. Other mosaics survive in the niches, and names carved by seventeenth-century Dutch and Flemish artists can still be read in some of them.

The ambulatory mosaics

4th century, on the vault of the corridor: geometric motifs, fruit, flowers, peacocks, doves and grape-harvest scenes. Among the oldest monumental Christian mosaics surviving in Rome.

The twelve pairs of columns

Granite shafts taken from an earlier building of the Roman period, carrying the dome of 22.50 m.

The twelve windows

Twelve arched windows light the central part, giving it considerable charm.

The niche mosaics

The handing of the keys to Saint Peter and the handing of the law to Saints Peter and Paul; at the sides of the entrance, Costanza and her husband Hannibalianus.

The sarcophagus copy

In the end niche; the original red porphyry sarcophagus is today in the Vatican Museums.

The Bent-vogels' names

Carved in some niches of the ambulatory by the seventeenth-century Dutch and Flemish artists, and still readable today.

The narthex with two apses

The link with the great cemeterial basilica, as in the Mausoleum of Helena on the via Labicana.

The lost dome mosaics

Removed on the orders of Urban VIII (1623-1644) because they were seriously damaged.