The list of units
Knights are fast and powerful. They are the first armored unit, and good at attack and defense. Knights will withdraw from combat if they are losing (unless fighting another fast unit).
A city must have both iron and horses in its Strategic Resource box to build knights.
Knights were heavily armored, mounted men-at-arms found primarily in medieval Europe. Like the samurai of ancient Japan, knights followed a strict code that covered their behavior both in battle and in their personal pursuits. Fighting astride powerful horses, armored knights had a distinct advantage over enemies on foot and remained the dominant force on the battlefield when battles were fought primarily hand-to-hand. Occasionally, brilliant infantry tactics allowed knights to be outmaneuvered, but it wasn't until the development of gunpowder that knights were rendered obsolete.