To the west of building 4 part of the road was found that connected Ostia and Portus. It is 10.50 metres wide, with a paved side for wagons and an unpaved side for pedestrians. It was probably built in the later first century AD and called Via Flavia, after a Flavian Emperor, or perhaps after Constantine (a coin of Galba provides a terminus post quem).

See building 4 for a plan of the excavations.