I've been pondering the boardgame Republic of Rome lately and have been thinking about doing something similar, but set around the fall of the western empire rather then it's rise. The game would start in the years 405-410 AD when the empire is on the verge of chaos. In Rome the weak child Honorius rules but the real power is with the barbarian magister militum, Stilicho who is living on borrowed time. In Gaul barbarians stand poised to pour over the border. In Britain Constantine III is about to start another civil war. Illyricum is under the control of barbarians who are about to pour into Italy and sack Rome for the first time in seven centuries. This is the choatic situation things start in. From here the players proceed controlling both powerful roman nobles and the barbarian leaders who are mobalized against the empire.
On the one hand every player would control a faction of Roman nobles like in the Republic of Rome board game. These characters have three stats representing their esteem with aristocrats, roman soldiers and barbarians (foederati). Through these characters, players attempt to control the key offices of the empire, governor of the provinces, magistar militum and the imperial throne. With many weak emperors there will often be powers behind the throne but a strong emperor could arise like Majorian if he is able to secure supporters to consolidate his rule. If you don't like the emperor then you can arrange for a coup against him with the support of the aristocrats or march against him from a governorship with support of roman or barbarian soldiers. Or maybe you will even have time to try to strengthen the state, retaking lost territories or trying to repair the damages of the war.
On the other side of things players also control barbarian leaders and work to carve out new lands. This is possible by direct invasion and capture of Roman lands, but it is also possible to go with a diplomatic route, like the Visigoths took when they accepted foederati status and resettled Aquitaine. Or you can just pillage anything in sight like Huns for immediate glory (and to undermine the power base of your fellow players). Control of a barbarian nation can be lost when a leader dies or is usurped, so it will take care to get the most out of this unpredictable resource.
The game ends when 20 turns have passed, representing a century of time. Over the course of the game the players accumulate two separate scores, tallying their accomplishments as Romans and as barbarians. Depending on the state of the fate of the empire, these scores will be of different value. If Rome is fallen you are judged solely on your score as a barbarian and for anyone to have won they will need to have built a mighty kingdom and acquired much plunder. If the empire is somehow intact after a century (unlikely) then players are judged solely on how much they accomplished as Romans. If the empire has lost territory but still controls Italy when 20 turns have ended, then both scores will matter. It will be possible for no one to have enough score to count as a winner and it will be at least somewhat possible for two players to have enough score to be winners.
So, post here if you think the idea shows promise. I imagine that this isn't a period of history that people are the most familiar with, but I personally think it's a very interesting time period and would make for a very good forum game. I don't intend for knowledge of the history to be necessary to play this, the rules should guide you to understand what the mindset of the era should be. Any takers?