As I mentioned in my post on Sant Agnese, the Mausoleum of Costanza was reputedly built in the mid 4th Century to be close to the tomb of St Agnes. The remains of the earlier church dedicated to the saint can be seen adjacent to this structure. There’s some debate over who exactly it was built for, but the general consensus is that it was a mausoleum for the daughters of Constantine, Helena and Costanza (confusingly also known as Constantina or Constantia). The sisters’ bodies were brought back to Rome from Bithynia and Gaul to be buried here.
It’s a lovely example of early Christian architecture, a round mausoleum structure that might reference Constantine’s churches in Constantinople. While now a church, it was originally purely a place to honour the sisters. To add to the site’s history, it may have been built by the emperor Julian (Constantine’s nephew) for his wife Helena (it’s a tangled family tree). This would have been remarkable as Julian rejected his family’s Christian beliefs and was the last pagan emperor.
Points of interest include original mosaics (pay 50 Euro cents to illuminate them), including a very early depiction of Christ in the form that we have become used to, and a replica of one sister’s porphyry sarcophagus. You can see the originals in the Vatican Museums.
As with Sant Agnese Fuori le Mura, the site can be accessed via Via Nomentana.