Bit late, but here are some board games that have the same theme (barbarians trying to take down Rome)
I've never played them personally - but here are the boardgamegeek links:
-Catan Histories: Struggle For Rome
BGG Entry: http://boardgamegeek.com/boardgame/25234/struggle-for-rome
Modified Settlers rules where players control tribes attacking Rome. Gain points for looting, conquering cities. Can win through points, or gaining the title of successor of Rome.
-Lest Darkness Fall: Rome in Crisis 235-285 AD
Game Rules: http://strategyandtacticspress.com/images/File/LDF_eRules.zip
One player plays the Empire, the other the barbarian forces. "In general, the Germano-Parthian player is attempting to invade the Roman Empire so as to overturn the territorial integrity of its core area or reach and loot Rome/Ostia.
-Barbarian, Kingdom, and Empire
BGG Entry: http://boardgamegeek.com/boardgame/2641/barbarian-kingdom-empire
"Players represent barbarian hordes who sweep down from the steppes to overwhelm the remnants of the Roman Empire and then build strong expansionistic kingdoms among the ruins. These kingdoms grow into empires which become rich, corrupt, and the target of new waves of barbarian invaders. Being defeated is not the end of the game, as players may return to the fringes of civilization to amass a new horde of Huns or Germans. The unique play mechanism allows players to enter or exit at any time without disrupting the play or the victory conditions"
-Ultimus Romanorum - the fall of rome
Wargame covering the fall of the roman empire. Seems to go for VPs based around territorial integrity and the status of the leaderships of rome.
There are other games on BGG where you try as a barbarian to overthrow Rome, but have no rules posted/available, so did not post them.