Mausoleum of Santa Constanza and the remains of Constantine's funerary hall, where Costanza may have originally been buried.

What to See at Santa Costanza

The 4th-century mausoleum of St. Costanza is a round brick building with a small west porch. The building originally had a forceps-shaped atrium at its entrance and an external colonnaded ambulatory (traces of which can be seen in the piazza).

Inside, there is a simple altar under a central dome. The central area is surrounded by 12 pairs of Roman columns, which form a barrel-vaulted ambulatory around the outside. Originally, the walls were covered in marble.

Directly opposite the entrance, at the east side of the mausoleum, is a large niche containing a sarcophagus, decorated with reliefs of putti harvesting grapes (a common theme in classical art). This is a replica of the grand porphyry original that is now in the Vatican Museums, moved there around 1785. It was probably commissioned by Emperor Julian for his wife Helena. Constantia's tomb is believed to be the tub-shaped porphyry sarcophagus now in the left transept of St. Peter's Basilica, moved there in 1606.

The main highlight of Santa Costanza is the barrel vaulting of the ambulatory, which is covered in original 4th-century mosaics. As in the original dome mosaics, these display a fascinating mix of pagan and Christian symbolism and imagery. According to the scholar G. Mackie, Santa Costanza's art reflects "the emerging iconography of the Christian faith in its first years of legitimacy in the Roman Empire."1 The Rough Guide to Italy similarly comments that Santa Costanza "perhaps more than any other building in Rome illustrates the transition from the pagan to Christian city in its decorative and architectural features."2

Dating from the 360s or 370s, the ambulatory mosaics were designed in corresponding pairs leading towards the niche with the sarcophagus, where the flanking mosaic pair is the most elaborate. The pair by the entrance are a simple, geometric design; this is following by a pair with a circular motif with animals and figures. Next are scenes of grape harvesting, then roundels with a leaf design, busts and figures. The pair by the sarcophagus have branches, amphorae and peacocks. The imagery is capable of both pagan and Christian interpretation, which is representative of Constantine's religious policy.

In the east niche above the sarcophagus are the remains of a mosaic with black stars on a white ground and traces of a gold Chi-Rho. The north and south niches bear mosaics dating from either the 5th or the 7th century. They have been poorly restored, but their richly decorated border reveal the quality of the originals. The date and interpretation of these two mosaics have been the subject of much scholarly debate.

The south niche mosaic (left from the entrance) depicts the Traditio Clavium, in which Christ Pantocrator, seated on a globe, hands over the keys to the kingdom of Heaven to St. Peter (Matthew 16:9).