I don't know about you, but I think Cavalry based armies are just rubbish in Siege assaults, both defence and attacks.
Currently with my Saissaidn campagin, I can never win an assault, why? Simply, because one Plumptarii can kill 3 Levy Spearmen, which developes a huge challenge to me. My cav is supposed to outcast the Romans', though it doesn't. Those Romans has same cav as me and still very stronger infantry. Last time I got assaulted, my enemy had 2 ladders, 1 siege tower, and 1 Ram. I focused my 3 desert archers units on the Siege Tower with 'Fire Arrows' ability on and it was also attacked by 1 of the towers, hoping to burn it. Though, it easily managed to get to my wall, deploy 2 units, and didn't even get 1% damage. Those 2 units were fought by 2 Levy Spearmen, of course, the spearmen didn't hold for 2 mins. On the other 2 places, where each ladder depoys I had 2 Spearmen units ready to fight, and somehow, those coming out of the ladder managed to give me units a hard beating. My strong cav, which lies beneath, stood their with nothing to do. So any suggestions about how to handle assaults in such factions?? (I think this applies to Parthia, Scythia in R: TW)