The architectural complex comprises two separate, communicating blocks: the mausoleum of S. Alexander Pope and the cathedral of S. Pelino. The first one, to the right of the cathedral, is a rectangular hall, beyond which a small circular apse (usually closed). As far as S. Pelino is concerned, it is fairly certain that in 1075 Trasmondo, abbot of S. Clemente, ordered a total reconstruction of a cathedral next to S. Alexander and over the ruins of the previous church.
After lengthy building work, the church was consecrated by Gualtiero in 1124 and today maintains the Gothic lines with which it was built between 1229-1235. the main faĆ§ade is characterised by a single Romanesque portal whose piers and archivolt are decorated with foliage motifs pillaged from the multitude of Roman remains hidden in the exterior walls.
The basilica interior, a nave and two aisles divided y fourteen pillars, is covered by exposed trusses. The apse dome retains traces of frescoes that are also present on the nave walls and is illuminated by three windows. A handsome wooden choir stall made by Ferdinando Mosca in 1738 covers the lower part. The absolute masterpiece of S. Pelino is the ambo in recent years it has been recomposed on the fifth pillar to the right. The dedication inscribed around the sides of the lectern, under Bishop Oderisio of Raiano between 1168 and 1188, belongs to the same typology of the amboes of S. Clemente a Casauria and Santa Maria Assunta in Bominaco.