Setting design III and a lens.

With me set on a Roman-ish empire and it being the sole dominant power I need a reason for it to fall. I also need a history on it and its people. Which is going to be this posts main point.
I'll also get a on to my space born civilization.

So having decided upon a fall of Rome scenario and a big ol' evil empire I need to get done with my bad guys. I also want to note that I don't want anyone to be evil for the sake of evil and that every faction has a story.

First of all, the center of this empire will be Sol and Earth is the big candidate. As much as I'd love having Holy Terra as my great empire it's to much 40k for me. I decide on a terraformed Mars instead and it's a kingdom so... Regnum Mars. It even has the latin name and all!

The big question I need answered is how did they get to be an empire dominating everyone else? I figure these guys would be first in space, that way they could easily conquer places like Earth and whatever else colonies that were in Sol at their time. Then using the combined scientific knowledge of the whole solar system would be the next logical step! Bingo.
However I do not want Regnum Mars to be dominant so it will be necessary to have Rome actually fall, but just how long have they dominated?
Pharaonic Egypt collapsed after 3000 years as the Ptolemaic dynasty fell and Aegyptus was integrated into Rome, some ever argue that Egypt existed at the beginning of the stone age!
Imperial China collapsed in 1911 as it was split between Chairman Mao and Chiang Kai-shek, lasting from the earliest bronze age to 1911, again 3000 years.
Compared to this the Roman empire (Including Byzantine Greeks err Romans, well you know...) lasted 1960 years approximately. An impressive lifespan.

This also makes the element of being so far into the future that we don't know anyone anymore as seen in Dune and Foundation very relevant as epic empires seem to be at least in the 2k-3k years old. Add in some attempts at streamlining culture and I get the whole so far in the future that we don't know anyone anymore.
Regnum Mars will definitely be 3k years old (In advance of this post I have a timeline but my players will also be seeing this blog and I want it to be secret) to attain this feeling.

Next point: The fall of Rome was not quiet and one of the greatest threats back then was the Huns and in medieval times the Mongol horde brought fearsome nomadic hordes to Europe. I want something to mirror this and I talked about belters earlier.
Making my belters nomadic would be sensible, they would not regard the planets that make the others livelyhood as much more then cities to be plundered and in nature they would be so separated that they would not be regarded by their fellows as human anymore.

Looking at biotech I found a couple of biomods of humans that would definitely pass as humans living in space too long. I took some of the traits and made my third lens.