I'm trying to remember the name of this story, because it was awesome. Turns out the Roman Empire didn't really fall; it had just gone underground. Once spaceflight was invented, this hidden Roman Empire somehow established its own colony planet, and became the main rival of Earth.
The novel (actually a series of several) was good old fashioned fun; pistols, cutlasses, square-jawed space captains, and derring-do.
Can anyone help me out here?