Our excavations show that at some time in the later 4th c AD, the Severan amphitheatre at the Palazzo Imperiale was demolished in order to make way for an eastern extension (Building 6) of the villa complex (Period 5). Furthermore, there is clear evidence for the re-decoration of first floor rooms in an adjacent part of the complex (Building 8). It seems very likely that this rennovation to the Palazzo Imperiale reflect a renewal of official activity by imperial officials involved in coordinating the supply of imported food to Rome.
Evidence from our excavations and from surface materials collected during the 1998-2004 survey of Portus, suggests that the port continued to witness intense commercial activity until the mid 5th century AD. At this point, the port authorities established a wall circuit that enclosed all of the buildings that clustered around the Trajanic basin and the maritime façade on the western side of the Darsena. Traces of these were found along the northern façade of Building 5, and the eastern and northern sides of the Palazzo Imperiale (Period 6A). The intention of the port authorities was clearly to ensure that this innermost area of the port, which remained the scene of commercial activity crucial to Rome, was protected from external threats, and quite possibly the Vandal invasion and sack of Rome in AD 455. Another important discovery was the proliferation of well over forty burials within Building 5 during the later 5th and early 6th c AD (Period 6A and 6B), suggesting that it was no longer used for commercial storage.
By the 6th century AD, the Claudian basin had largely silted up and even though the port was the focus of a struggle between Byzantines and Ostrogoths during the Gothic wars (AD 535-553), commercial activity had now significantly diminished. Furthermore, the Palazzo Imperiale and Building 5 had been demolished by c AD 530 (Period 6C), and as far as one can tell, the adminstrative focus of the port had contracted to a reduced area around the Basilica Portuense.