From a few literary sources we know that the Emperor Constantine donated a church to Ostia. This is described at length in the Liber Pontificalis (Silvester, 314-335 AD), where donations by a certain Gallicanus are also recorded. The church was dedicated to Peter, Paul and John the Baptist. The dedication to the latter and the donation of a baptismal installation indicate that it was the church of the Bishop of Ostia, who from 336 AD consecrated the Pope. In the Acts of Saint Gallicanus (Acta Sanctorum, June, V) this Gallicanus is mentioned as the sole builder of a church of Saint Lawrence in Ostia. In the Acts it is said to be near a gate called Laurentia. This might be the same church, erroneously assigned to Laurentius by using the name of a city gate, Porta Laurentina, that led to the Laurentine territory to the south of Ostia. Gallicanus is either Ovinius Gallicanus, consul in 317 AD, or Flavius Gallicanus, consul in 330 AD. He is said to have established himself in Ostia, and to have extended his house in order to receive pilgrims.
A geophysical survey (the combined use of aerial photographs, magnetometry, and electrical resistance tests) of the unexcavated areas of Ostia led to the discovery of a church that may well be that of Constantine. The survey, under the direction of the German Archaeological Institute in Rome (Michael Heinzelmann and Franz Alto Bauer), was begun in 1996. Several small trenches were investigated in 1998 and 1999. Excavations on a larger scale took place in 2023. The building is situated to the north-east of a secondary gate at the south end of Via del Sabazeo, so indeed leading to the Laurentine territory (and not to be confused with the gate that the excavators have called Porta Laurentina, further to the west).
Region V with new discoveries, resulting from the geophysical research by the German Archaeological
Institute in Rome. The Christian basilica is indicated in blue. It was erected on top of a building
from the Hadrianic period, indicated in red. Numbers indicate trenches. The secondary gate at the south
end of Via del Sabazeo is at nr. 11. Plan: Michael Heinzelmann.In front of the church is a courtyard, the atrium. Between Via del Sabazeo and the atrium was a small square from which the atrium was reached. The actual church has three aisles, the central one with an apse. The length of the central aisle plus the apse is 51.45, the width of the three aisles is 23.20. The total length including the atrium was 77.50. Very little remains of the walls. There were fourteen columns on each side of the central aisle. The building must have been more than 14 metres high.
Plan of the Christian basilica (blue) and older buildings (grey). Numbers indicate trenches.
Plan: Michael Heinzelmann.The Basilica was erected on top of a Hadrianic building. The atrium reuses its courtyard. The Hadrianic building in its turn was built on top of a building from the Augustan period.
The pottery found in the trenches gives a Constantinian date to the church: c. 320-340 AD. In the later fourth or early fifth century the floors were raised. A rectangular chapel for baptism with an apse at the east end, set against the south wall of the atrium, was added in the same period. Some early Mediaeval sherds were found inside the church, and in this period the apse at the end of the central aisle may have been rebuilt. In the late fifth to seventh century domestic structures were built near the church, that was slowly being abandoned. In the eighth century the building was systematically plundered and in the late eighth and early ninth century the walls collapsed, shortly before Gregoriopolis (modern Ostia Antica) was built.
The results of the geophysical survey by Michael Heinzelmann.
View of the excavations in 2023. Photo: Parco Archeologico di Ostia Antica.
View of the excavations in 2023. Photo: Laura Nicotra.
Reconstruction drawing of the basilica. Heinzelmann 2020, fig. 120.
