This round building with a dome was built in the III century as a mausoleum of Emperor Galerius. But the emperor was buried in another place, and the Rotunda was converted to a Christian church. Thus, it is one of the oldest church buildings in the world! At the end of the XVI century rotunda it became a mosque, while the minaret was built.

Since 1912, the Rotunda is a memorial museum. The monument had marble cladding, which has not survived, and is decorated with wonderful mosaics. It is not known exactly when they were created. His mosaics are considered among the oldest surviving wall mosaics and probably belong to the time when the monument was converted into a Christian church, that is, to the IV century.