The basilica represents a key monument of early Christian church architecture: among the Constantinian church foundations, it is the only one to have remained entirely free of later structural alterations. As such, the building at Ostia allows the original architectural type to be analysed in its entirety for typological, architectural-historical, and liturgical questions. Moreover, it constitutes the first known example of a “standard” basilica—one that was neither constructed as an ex-voto foundation nor designed as an architectural shrine around a venerated tomb or as a cemetery church.
Since the summer of 2023, a team from the Department of Christian Archaeology at the University of Bonn, in cooperation with Classical Archaeology at the University of Cologne and the German Archaeological Institute, Department Rome, and supported by students from the universities La Sapienza, Roma Tre, and the Pontificio Istituto di Archeologia Cristiana, has been conducting the excavations in the area of the episcopal church.
The first campaign focused on the eastern end of the church, including the apse and presbyterium. It yielded important insights into the building’s typology, chronology, and liturgical furnishings, including the identification of a previously unknown construction phase involving the installation of a solea in the nave, as well as indications of an unusual apse shape in the Constantinian basilica. The second campaign, carried out in the summer of 2024, centred on the western part of the basilica and the transition to the atrium. In addition to a largely preserved floor mosaic from the Constantinian period, collapsed arcade arches and an Ionic capital came to light, providing further insights into the design of the sacred interior. The third excavation campaign in the summer of 2025 examined the area south of the basilica and the atrium up to the city wall. The main focus was the baptistery and the presumed episcopium. The existence of the latter could be confirmed through the discovery of a large audience hall (aula) with a mosaic floor and marble wall decoration. The investigation of the transition between the atrium and the street, as well as the eastern sector of the episcopium, is planned for the coming years.