I love to play ROME Total War and I just finish ERE campaign. I follow some of this posts, but I guess a I was lucky. I found out soon it isn’t a good idea to fight a horde in a classic battle. So, I reinforce Constantinople and Sirmium fast and I raised two full armies (main force of heavy infantry (commies, limitanei, later replaced with legio lanceri, lot of eastern archers, few light cavalry units, heavy mercenaries units). This armies was placed on the northern bridges and the hordes have something against it. The hordes attacked every turn this bridges and I won most of the battles. Remember this: YOU HAVE RESERVES, THEY DON’T. After many turns the barbarian were out of heavy troops, the only remains was horse archers and generals. Now I detached the cavalry units, I make a single army and go after them. Soon, I destroy the Goths, the Vandals, the Sarmatians and, finally, the Huns. I was lucky when at the beginning the hordes battle each other. I make an alliance with the Goths and destroy the Sarmatians. The Vandals were decimated by the Huns and I hunted down the remaining forces. The Huns were the hardest one to battle, but I have already experienced units at my disposal and a take fewer casualties as at the beginning. At the same time, I have to deal with the Sassanids. I applied the same “bridge tactics”, but the main Sassanid armies were a joke. The Clibinari was responsible for 90% of the causalities suffered in the battles. I was able to purchase 2 Ballistae and I go on the Clibinari hunt. The Sassanids were easy to conquer, but hard to keep. I have revolts in all the settlements and this blocked my eastern army for the rest of the game. The Western Empire was disintegrated in to several Rebels towns. Rome, Salona, Carthage and others was this kind of towns and I go and besieged them without going to war with WRE. After I conquered Rome, WRE attack me, but it was to late for them. With two huge and full armies (Onagers, repeating ballistae and others “goodies”) I take the rest Italy and several others towns.
For military purposes I upgrade Constantinople, Sirmium, Antioch and by mistake Alexandria. With the army of Alexandria I take Carthage and go to Rome. One of northern armies landed in Italy at the same time and Game Over.
For the rest of empire I make money.
Use Assassins to kill enemy diplomats and generals. Make alliances with the Hordes but don’t let them pass the bridges in your territories. Blocked them with the armies.