The Archaeological Area under the Cathedral is located in Concordia Sagittaria (VE), and develops below the Cathedral of Santo Stefano and the Cardinal Costantini town square. It preserves remains from the Roman age and the well-known paleo-Christian monumental complex.

Related to the Roman area are a large paved stretch of the Via Annia, the ancient consular road, which connected Adria to Aquileia, and part of the commercial warehouses ( horrea ). On the southern side of the road is the early Christian ecclesial complex. It includes the Basilica Apostolorum , with three naves, entirely covered with a mosaic carpet and the trichora martyrum , a three-apse building dedicated to the cult of martyrs. It was discovered and excavated several times starting from the fifties of the last century. Its first layout dates back to the end of the 4th century AD and it remained in use, with successive expansions and embellishments, until well into the 6th century AD, when fires and floods decreed its end and abandonment.