Plz. save yourself from exceedingly high casualties by NOT attacking full strength pikemen with anything except attackers with a same or higher (3+) attack value. And be aware of the defensive bonuses the pikemen might have. I have found, more often than not, that cities defended by pikemen often produce longbowmen. Horsemen waiting 2 tiles away from a city are good for picking-off emergent longbowmen...if you've succeeded in pillaging the roads to that town. Otherwise, I would suggest you use your horsemen to perform a pillaging blitz through the offending civ. while you wait for Chivalry. Let the cities languish and drop in pop. to below 6...thus decreasing the def. bonus.