it's interesting that somebody mentioned the infantry issues of Persia in Rome and BI. My tricks have included chasing enemy forces into the vicinty of the city I wish to take (the ERE falls for this trick all the time in BI) or using spies to undermine the city's loyalty or break the gates open. (Used with devastating effect against the Seluekids in SPQR) I never include infantry in my field armies with either Persian faction. The Persian infantry are good for garrison duty however.