The church shows clear influences from the workers who were called to build it, and which belonged to the
Lombard and
Pisane schools. The portico, inspired by French models, has a lower storey with three rounded arcades, two of which included
mullioned window (the left one closed). The middle arcade leads to the
narthex, which has six
groin vaults supported by cruciform
piers. On the narthex' right side is a staircase leading to the upper floor with three rooms, the central of which, provided with an altar, was the private chapel of the bishops of Bisarcio. Behind the altar is a mullioned window opening towards the interior of the cathedral, sided by two decorative lozenges which can be seen also on the exterior walls of the
apse, and are typical of the Pisane Romanesque style. The right room houses instead a characteristic
mitre-shaped fireplace. From the narthex is also accessible the true interior of the church, which has a nave and two aisles divided by columns, with a semicircular apse. The nave is covered by wooden
trusses, while the aisles are groin-vaulted. Light is provided by narrow single mullioned windows, six in each side plus another in the apse and two at the end of the aisles. On the southern side is a bell tower, whose upper part is missing after crumbling down in an unknown date. It has a square plan and is decorated by false columns and
Lombard bands, which are also present on the church's external sides and apse. ==Sources==