Santa Costanza is a 4th century church in Rome, Italy, on the Via Nomentana, which runs north-east out of the city, still under its ancient name. According to the traditional view, it was built under Constantine I as a mausoleum for his daughter Constantina (also known as Constantia or Costanza) who died in 354 AD. His other daughter Helena, wife of Julian, who died in 360 AD, was also buried here. In the early Middle Ages it was dedicated as a church to Santa Costanza (Saint Constance).

The fabric of Santa Costanza survives in essentially its original form. What were probably magnificent decoratively coloured stone panels on the walls have gone, no doubt to decorate later buildings, and a few of the mosaics have had some minor damage and incorrect restoration but for the most part it stands in excellent condition as a prime example of early Christian art and architecture. It was built next to, and in connection with, the 4th century basilica of Santa Agnese or Saint Agnes, to which it was attached mid-way along the liturgical north side. Both buildings were constructed over the earlier catacombs where Saint Agnes was buried. Only a long section of the main outer wall of the basilica survives, from the north side and the apse at the eastern end. In the 7th century the present church of Sant'Agnese fuori le mura was built a few metres away, as the Constantinian basilica had decayed and was considered too large to refurbish. One key component which is missing from Santa Costanza is the art of the central dome. But in the sixteenth-century, drawings were taken of this central dome so the artwork can be reconstructed and examined. One key component which is not missing, and is extremely valuable to both the Art and History disciplines, is the large porphyry sarcophagus of Constantina, which was moved in the Renaissance to the Vatican Museums, where it is on display. Overall, most of Santa Costanza has been preserved extremely well.