The remains of a monumental hall belonging to a 4th-century episcopal palace have been discovered at Ostia Antica, Romes ancient port town. The base of the structure is eight by 20 meters (ca. 26 by 65 feet) and the walls were an estimated eight meters high. This is an extraordinarily large space, and it was richly decorated with mosaic floors and marble panels. It is one of the oldest Christian complexes ever discovered the environs of Rome, and its rich decoration and expansive facilities are on a scale previously unknown in the Constantinian period.The archaeological remains of the 1,700-year-old structure lay hidden just inches below the topsoil, scraped and dislodged but not severely damaged by centuries of agricultural activity just above it. In fact, farming helped preserve the remains.Ultimately, it was fortunate that the farmers continued to use the land until the Ostia Antica Archaeological Park near Rome was established. Here, no buildings interfere with our excavations we hardly have to take graves or anything like that into consideration, says Prof. Dr. Sabine Feist of the Department of Christian Archaeology at the University of Bonn. A favorable situation for research and not only for that reason: We know of other churches from this early period, but these were completely altered in the Middle Ages. That didnt happen here either.The newly-discovered structure is adjacent to a monumental church complex discovered by geophysical surveys in 1996 and excavated in 2023-4. The church was built around 330 A.D., late in the reign of Constantine (306-337 A.D.) on the remains of a Roman insula (apartment building). Measuring about 50 by 80 meters, the church complex covered 4,000 square feet and included am adjacent bishops residence.For such an elaborate complex to have been built when Christians had only recently been granted legal rights (Edict of Milan, 313 A.D.) and freedom of worship is evidence of a well-organized Church apparatus, capable of emerging from the penumbra of private and literal underground spaces straight into sophisticated, large-scale architectural developments.The Bishop of Ostia was an important church leader in the Early Church. He held the position of Cardinal Dean, charged with convening the conclave of cardinals to elect a new pontiff after the death of a Pope. The exact location of his titular church and residence were unknown until the 2023-4 excavation confirmed the identity of the building complex.