Location of the Frigidus River

[Tormenta]

Perhaps the 'extra' walled areas could be used to house cattle, or perhaps civilians in case of emergency? Or perhaps a reduced defensive force?

The cattle options is also a formal explanation, but is also accompanied by the possibility of being used for cases of emergencies.
For hosting the local population of course, can be a possibility and also for hosting a defensive force. This can at least stop for a few days the advance of a barbarian force or a roman one to entering into the north Italian plains.
Not much articles are available on this(as far I know), but in the last times much effort is being putted to better present and preserve the remains.