The Neonian Baptistery is one of the most ancient monuments of the city of Ravenna. It was commissioned by Bishop Urso and probably built at the beginning of the 5th century like the nearby cathedral. During the episcopacy of Neon (450 - 475), the baptistery underwent many restoration works that ended with the reconstruction of the cupola and the realization of the interior decoration, still present today.

The brick building is octagonal in shape and has four big external niches. On every side, rounded windows and underground doors open to the inside of the church.

The interior of the baptistery consists of two rows of arches put one above the other. Its decoration is divided into three tiers, the lower one covered with marble pieces, the middle one with stucco-works, while the upper section is adorned with mosaics of Hellenic-Roman influence. At the centre of the dome, a big medallion frames the Baptism of Christ, depicted as a young man immersed to the hips in the sheer waters of the river Jordan. This is one of the oldest mosaic scenes of the Baptism of Christ housed inside a monumental building. The images of the twelve Apostles, divided into two groups led by Saint Peter and Paul, revolve around the central medallion, standing out against a blue background. A second ring shows eight exedrae that cover thrones and altars and symbolize the concept of heavenly city and the spread of the Christian doctrine.

In the middle of the building, an octagonal font of Greek marble and porphyry rebuilt in the 16th century still preserves some of its original elements from the 5th century.

In the early 20th century, Carl Gustav Jung, one of the founders of psychoanalysis, was particularly impressed by the magic of these decorations.