The present parish church (a cathedral until 1828) is a basilica with three naves, that originates, according to two different theories, either from Early Christianity or from the second half of the 8th century. Traces of these older periods are visible along the northern longitudinal wall, where Early Christian window frames were discovered in 1972.
The sacral complex also incorporated a baptistery and an episcopal palace, which were torn down in the second half of the 19th century. The old bell tower that was leaning against the cathedral front was replaced by a new, free-standing campanile in 1874. The church building was thoroughly renewed in the years 1408, 1580, 1746 and 1775. In the Middle Ages, its interior was painted with frescoes, as fragments at the southern side altar show. The present, Neoclassicist façade was finalized in 1935. The interior of the church is dominated by a Baroque altar and a raised, deep choir, under which an (Early) Romanesque crypt is located.