The patron saint of Castel Volturno is Saint Castrese, credited with spreading Christianity in ancient Volturnum as early as the 4th century: the town was an episcopal seat from the 5th century, as attested by the subscriptions of Bishop Paschasius to the Roman councils of 499, 501 and 502.
After 856, the Lombard bishop Radiperto had a fortified castle built on a surviving arch of the Domitian bridge and rebuilt the church holding the saint's remains. At the centre of the castle's walled borgo now stands the Chapel of San Castrese, dedicated to the town's patron, whose walls are decorated with frescoes recounting his life. The town also holds the church of the Annunziata, built in the 16th century and reworked several times over the centuries.
