I get the sense that you're going for a China analogue. The problem with that is that Rome's geography makes it nearly impossible for it to isolate itself.
Look at China: Mountains to the south, a desert to the west, frozen tundra to the north, one coastline.
Now look at Rome: Open plains to the north and east, multiple coastlines, access to the Atlantic and Indian ocean.
China could easily seclude itself by building a wall to the north and stationing some troops. Rome can't do that. Its northern border is way too large and easy to cross.