Interesting how some historical places, even relatively recent, can be lost to time. It reminds me that no one is quite sure where the Rubicon was when Caesar crossed it.
Not only that, I don't think the Rubicon even exists now, the wikipedia page has a quite extensive discussion about it, but a quick online search turns up more. Basically, though, the law about crossing the Rubicon under arms was apparently never enforced, against Caesar or anyone else, and throughout the imperial period the Praetorian Guard -- a full legion that was at least supposed to be the bodyguards of the Emperor as well as the local gendermes for Rome -- were stationed right in the city, fully armed. The law was probably not ancient, and very likely wasn't even a law, just more of a guideline or tradition.
Well, the Rubicon meets the sea, perhaps in a different spot today, but this is how it now looks:
https://www.hotelfantini.it/gatteo-mare_it.php