The Arian Baptistery stands in a small square next to the old Arian cathedral of Santo Spirito in Ravenna, Italy. It was an example of Arian Christian art, which rarely survived Late Antiquity.
In the 5th century, Ravenna was ruled by Theoderic, a Goth who ascribed to the Arian form of Christianity. Declared a heresy at the Council of Nicea in 325, Arianism is the view that Christ, while divine, was created by the Father and is therefore inferior to him. The orthodox view holds that Christ is equally divine ("of the same substance") as God the Father. Theodoric built a new Arian cathedral (the Basilica Spirito Santo) with its own baptistery towards the end of the 5th century, not long after Ravenna's Orthodox Neonian Baptistery was built. It is quite similar to its orthodox predecessor, including the mosaic in the dome.
The Byzantines took Ravenna in 540, bringing Arian and barbarian rule in Italy to an end. About 10 years later, Emperor Justinian gave the Arian Baptistery to the orthodox (Catholic) community of the city, who turned it into a church called Santa Maria in Cosmedin.