"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." Wikipedia.
What Wikipedia fails to tell you is that Santa Costanza is utterly beautiful. I may be developing a thing for round churches, but this one is a belter. Take a bunch of 50c coins to put in the meter to light up the mosaics. The church is just behind Sant Agnese Fuori le Mura.
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