I just tried the battle of carrhae again and WON! Woohoo.

Seems like the secret is obvious: get out of testudo formation asap, and form a line facing the cat charge that is two units thick. Forget about the archers. At the same time, send your two cavs forward and to the sides to chase away the cavs while getting into position to charge into the back of the cats after they charge your infantry.


As the cat appraoches, counter alt-charge them with your first line of cohorts, and regular charge the second line with the javlins The cats should get just deep enough within the first unit but not make it to the second. This allows the two flanking rear units to wrap around and attack the flanks of the cats. Then alt charge the two middle coharts in. They won't do much fighting, but are needed when the cav archers charge. you will counter alt charge them as they charge you.

in the meantime, after charging into the back of cats with your cavs, pull out far enough to chase away the front side archers, then charge back into the back of the cats. after the rear cav archers charged and gets stuck, you only have to worry about the two side cav archers, who are only hitting your wrap around flanks.

note that since there's periodically one side open, the units has a means of routing so "fight to the death" won't kick in.

eventually one side of the cats will be wiped out, freeing up some spare coharts to handle charges from the side cav archers. attack the flank/rear of the cats until you see the cav archers charge, then counter charge them with your cohort unit. pull out your cavs from the front and move them to the sides. one will keep away cav archers while the other will charge into the back of the charging cav archers.

after that, use your own judgement. There should be one two mostly-dead cataphracs unit left and a few cav archers units that are out of ammo by now. When the last cat charges you, counter charge with your two rear cohorts. Charge your side cav at the old cats that the coharts had been engaged with. The cats should be chasing your charging coharts, so a flank charge should take out most of the remaning ones. Follow up by sending whatever you can spare to finish off the cats. counter charge cav archers as needed. it'll just be mopping up from here. Of course use the general's rally if you see your units routing... you need every one!

I ended up with about 5 cohart units and 1 cav unit left, but didn't get out of testudo formation fast enough. (two the units stayed in testudo and won't get out, and were killed pretty quickly.) So if everything happened right, you should have a lot more to spare.