The list of units
The Pikeman is an excellent defender.
A city must have iron in its Strategic Resource box to build a pikeman.
The growing deployment of knights on the battlefield demanded that foot soldiers develop new means of fighting that would lessen their vulnerability to mounted opponents. One of the best ways to do this was to lengthen the reach of the infantrymen by arming them with long, sturdy spears known as pikes. Massed infantry armed with pikes -- particularly in conjunction with archers -- managed to even the battlefield odds. Armies equipped in this manner were able to hold their own until the invention of gunpowder made archers, pikemen, and knights a thing of the past.