Archaeological remains inside of the church, begun in 1969 and whose results have been visible to the public since 1992, have brought light to the twelve centuries of the history of the city, in five layers. These go from the remains of a Roman Domus from the 1st century B.C., to the remains of Roman thermal baths, to the remains of an Early Christian basilica from the 4th-5th centuries A.D., to those of the Baptistry and the crypt from the 9th century A.D., to the church above whose construction begun in the 12th century together with the new Baptistry. This is that which we see today, but its façade was created in a late-Renaissance style at the beginning of the 16th century.