This is not an uncommon occurrance.

Unfortunately I've reached the mopping up stage of my Rome:Total War campaign. My Spanish troops are busy mopping up the final few provinces North of the Black Sea (97/102 provinces pwned) and therefore this does not pose a sufficient challenge. I have recently found a neat trick - a double row of Bull Warriors (Spanish pilum armed troops) set to "Fire at Will" is likely to kill any Roman Legionaries before they get to mix it.

I think I'm going to have to try out that copy of Medieval 2:Total War, that has been sitting unused on my PC for some time.