The fabric of Santa Costanza survives in essentially its original form.
Despite the loss of the coloured stone veneers of the walls, some damage to the mosaics and incorrect restoration, the building stands in excellent condition as a prime example of Early Christian art and architecture.
According to the traditional view, Santa Costanza was built under Constantine I as a mausoleum for his daughter Constantina, later also known as Constantia or Costanza, who died in AD 354.
However, more recent excavations seem to date the existing church to the time of Emperor Julian (r.
Santa Costanza is a 4th-century church in Rome, Italy, on the Via Nomentana, which runs north-east out of the city.
It is a round building with well preserved original layout and mosaics.
The original structure containing the tomb of Helena might be located underneath the current church, as a possibly triconch-shaped structure has been partially excavated in 19 and computer-reconstructed by David J. That could suggest that the current church is the second Christian building on the site, and may be some decades later than traditionally thought, being built as a mausoleum for Constantina's sister Helena in the reign of her husband Julian the Apostate.
The larger of the two porphyry sarcophagi there would belong to Helena, and the smaller to Constantina, the opposite of what has been traditionally thought.
If that should be the case, then the building was mainly dedicated to Helena and only secondarily to her sister Constantina, whose sarcophagus was brought into the new building from an earlier structure.The earlier triconch building of the 330s was probably indeed built for Constantina, but she later had to take second place to her sister; as Constantina's fame as a saintly figure developed in the Middle Ages, their roles became reversed in the popular mind.The mausoleum is of circular form with an ambulatory surrounding a central dome.The vaults of the apses and ambulatory display well preserved examples of Late Roman mosaics.It has been built adjacent to a horseshoe-shaped church, now in ruins, which has been identified as the initial 4th-century cemeterial basilica of Saint Agnes.
(Note that the much later Church of St Agnes, still standing nearby, is distinct from the older ruined one.) Santa Costanza and the old Saint Agnes were both constructed over the earlier catacombs in which Saint Agnes is believed to be buried.