One of Rome's most ancient churches, the Mausoleum of Santa Costanza is more than a building. It's a treasure trove of some of the earliest Christian art in Rome.
According to tradition, the mausoleum was built in the 4th century for Costanza, one of the daughters of Emperor Constantine (you know, the guy who legalized Christianity). In reality, it was probably built for her younger sister Helena, and Costanza's body was transferred here to lie with her. (Details, details).
Most importantly, though, the mausoleum was decorated opulently—as would befit the daughter of an emperor. (Helena also was married to the emperor Julian the Apostate, so she was doubly important). That explains the mosaics that decorate the church's ceiling and walls, which, as 4th-century mosaics, are some of the most important early Christian art in the world.
Interestingly, the ancient mosaics also illustrate the shift from pagan to Christian art, and how heavily the early Christians were still leaning on pagan traditions. The scenes of grape harvesting and the details of peacocks, amphorae, and vines all had their roots (no pun intended) in pagan art. (Since a major part of Constantine's policy was adapting pagan traditions to the new, Christian ideas, this, of course, is a fitting symbol of the empire's politics at the time).
The other cool thing about the mausoleum is its shape. It's round, with twelve columns and twelve arches holding up a twelve-windowed dome (yeah, twelve is kind of symbolic). In fact, Santo Stefano in Rotondo only wins the title of being an "older" round church in Rome because of a technicality: It was built in the 5th century as a round church, not as a mausoleum, while Santa Costanza became a church officially only in the 13th century. Either way, the whole round-church aspect is pretty neat.
And if you're wondering where the sarcophagi of Costanza and her sister are today, well, you have to get to the Vatican.The one you see here is a copy of the red porphyry original in the Vatican museums, probably for Helena (pictured below), while Costanza's tomb is probably in St. Peter's Basilica.
Santa Costanza is located at the intersection of Via Nomentana and Via di Sant'Agnese; here's a map of the location of the Church of Santa Costanza. The mausoleum is open Tuesday through Saturday from 9am-12pm and 4pm-6pm, Sunday from 4pm-6pm, and Monday from 9am-12pm. Since it's right next to the Basilica of Sant'Agnese fuori le Mura and the Sant'Agnese catacombs, coordinate your visit with a stop there, too.
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