Because of the importance of the Appian Way, that just here entered the town, the whole area was concerned with great traffic movements, especially during ancient Rome. It seems that close to the door there was an area designed for parking of the private means of transport (belonging to high rank personalities which could afford it) that accessed the town from here; it was what now could be defined a "park and ride", since the transit of private means within the town was usually not allowed. This rule probably was effective also for the members of the Imperial family, whose private means were parked in a reserved area (called Mutatorium Caesaris) just a little farther at the beginning of the Appian Way.
