Excavations conducted between 1995 and 1997, during the refurbishment of the heating system and flooring of the Parish Church of St. Stephen, confirmed its early Christian roots, unveiling evidence of three distinct churches that stood until the late 16th century: St. Stephen, St. Agnes and St. Vincent. The area where the three churches were erected originally housed a Roman villa constructed in the 1st century AD. Later, around the mid-5th-century, a mausoleum was carved out of the villa, which was later transformed into an oratory in the 7th century with the addition of an apse. Following the complete demolition of the early medieval oratory, a church featuring three naves and two apses was built at the turn of the 10th and 11th centuries.
Except for the bell tower and certain parts of the masonry, the Romanesque church underwent a significant downsizing and reconstruction in a Baroque style in 1665. Finally, in 1896, the place of worship was extended westwards with the construction of a new apse to replace the previously demolished eastern apse, making way for the new façade. Of the three original churches, only St. Stephen stands today, while St. Agnes and St. Vincent were demolished at the close of the 16th century due to safety concerns. St. Stephen was elevated to Parish status by Cardinal Borromeo in 1566. Several important finds were made over the years during the excavations. Notably, three marble columns dating back to the 5th or 6th century from the early Christian mensa of St. Agnes are today preserved in a room adjoining the sacristy.
Other important artefacts substantiating the early Christian origins of the church include three reliquary urns: the first crafted from marble, the second from chalky stone and the third fashioned from silver, all dating back to the late 4th or 5th century, in addition to three 5th-century votive silver laminae depicting a saint. Two other fragmentary inscriptions dating back to 491 and 539 were found between the 18th and 19th centuries, and two fragments of another slab—with inscriptions to “vir illustris Pierius” and “tus presbiter”—surfaced during the restoration works in 1896.