The parish church of Sant Pere was built in the northern part of the enclosure. Of the original construction only the trilobal apse remains from the beginning of the 6th century, which, like the apse of the Santa Maria Cathedral, was reused as the head of the 12th century Romanesque construction. It was a three-nave building with a three-lobed head.
At a later stage (7th-8th centuries), the presbytery was re-floored with a mosaic and the mural altarpiece of Saint Peter was built in the central lobe.
The lower part is rectangular and represents the Crossing of the Red Sea. The upper part, in a semicircular shape, has a five-inch angels and cherubs decoration in the foreground with St. Peter, St. Paul and the Tetra-morph, the 4 evangelists’ symbol.