> (Rome itself — the exception that proves the rule

You really have to explain specifically what you mean by this phrase, or else it's typically just saying you don't actually understand the rule or the exception.

It sounds like you're claiming Rome succeeded for reasons that overcame its geographical disadvantages, and due to this growth protected itself from naval invasions. But Rome was not a maritime power during its early republic period, let alone earlier. So why didn't Carthage or anyone else just sail upriver (Rome was not on the coast, just to clarify the context) and destroy Rome? How did Rome succeed in the first place to become a maritime power capable of defying southern Italy's geography?