The Neonian Baptistery, also known as the Baptistery of the Orthodox, dates back to the 5th century. It takes its name from Bishop Neon, who continued its construction after his predecessor Orso. The name of the Orthodox, however, is to be understood according to the meaning of the time, which meant the Christians of the "righteous" doctrine as opposed to the Arian heresy. The interior is notable for the decoration of the mosaic dome dating back to the time of Bishop Neon. Within three concentric rings various subjects are represented: in the central circle, on a gold background, is the scene of the Baptism of Christ; the second band presents the twelve apostles on a blue background, holding crowns to be offered to Christ; the outer ring, on a blue background, presents a series of tripartite mock architectures.