The present church is baroque in style, but contains some works of art of earlier periods.
The cathedral has a Romanesque Gothic portal of 1332 by a Roman marble worker named Deodatus, and the interior is decorated in the Baroque style, but still retains the pointed vaulting of 1154, introduced into Italy by French Benedictines; it contains a splendid silver antependium by the 15th-century goldsmith Nicolo di Guardiagrele (1433-48).
Agatha, containing the relics of the saint, retains its three original Norman apses (1091), but is otherwise a large baroque edifice.
The interior was restored in the baroque style in 1712.
Two baroque chapels were added in the 17th and 18th centuries, which are fortunately shut off from the rest of the church.