I want to know how far out of the field a concept this is. It'll ultimately affect the layout of a city map, which is reason enough to ask the question here I think.

I have a city in my campaign, the center of it actually, that has become a sort of nexus for world trade. It was originally a far flung colony of an empire, but the empire fell and the colony grew into an independent city-state.

The city is surrounded by sea and wilderness. Primitive cultures abound, but the nearest kingdoms and young or crumbling empires are either across the sea or much further inland. The only reason the city has gotten it's reputation for trade and not been forgotten entirely is it's position to facilitate trade between those isolated inland cultures and those across the seas.

Why this would matter for a city map? I was thinking of keeping major defensive measures to a minimum. A wall to protect against the primitives, and a small military force, but no real standing army. The idea is that the real threats, all of whome certainly covet the wealth of the city, simply won't allow any of the others to claim it for themselves. Independently it poses no real threat and everyone gets rich... Those making the money would prefer it go undisturbed.

Now. Reality check. How plausible is that?