The church we admire dates back to around 1100. It has a longitudinal plan developed into three naves, each ending in an apse. By observing the walls, it is possible to appreciate various construction techniques: masonry made of squared limestone blocks can be identified, along with courses of bricks in the central sections and in the arches, and finally small tuff blocks in the upper parts. The naves are separated by a series of arches resting on four reused columns and two piers on each side.
Particularly noteworthy are the Ionic-style capitals of the colonnade, dating to the 3rd century AD, to the Severan period, whose forms were reproduced in two other capitals from the medieval period—namely, the first two on the right-hand side. Looking upward, on the first window of the left wall, one can make out two fragments of a sarcophagus: specifically, two portions of a lid, the first placed vertically and the second reused as the window’s lintel. On the latter, a series of dolphins swimming among the waves is carved.
At one time, the entire church was richly adorned: the floor was made of marbles of various colors forming numerous geometric patterns. The central space was probably occupied by the schola cantorum, composed of small marble pillars and partition slabs. Some fragments of these elements are now scattered throughout the abbey, reused as building material. The walls, too, must have been entirely decorated with frescoes.
