The Knight is the fast unit of High Middle Ages. It has moderate damage and defense. It is effective against the ranged unit class but is vulnerable against the light class.
Compared to the Heavy Cavalry of the previous age, Knights gain +4 attack, +4 defense, as well as a nice movement boost of +2. As a result, for the first time, fast units have a higher defense than same age light units.
It is worth noting that at this point, Fast units start becoming a decent unit for stats. They have enough attack and defense to be used regularly. They also have a special ability, Chivalry, which gives them a +3 boost in both Attack and Defense only if it is the only unit with Chivalry (i.e. Knight and Heavy Knight) in army.
Knights should be used singularly in battles, to allow for Chivalry to take effect. Having multiple Knights requires all but one Knight to die before Chivalry takes effect.
Knights should be used to charge into enemy lines and kill ranged and artillery units.
Against Same Age Units
The Berserker can easily take down Knights, while Knights struggle to do high damage against them. Knights should avoid combat against enemy Berserkers unless they are finishing off a wounded Berserker, or if there are no ranged or artillery units to attack.
Knights are very effective against the Crossbowman. The high movement speed allows them to reach the other side of the map in two turns, which means Crossbowmen cannot take full advantage of their ranged attack. The defense points against ranged units allows Knights to take multiple hits.
Knights are not the best choice to attack Heavy Infantry, due to the high defense that Heavy Infantry has. The Crossbowman is almost always a better choice to fight armies with Heavy Infantry. However, if needed, the Knight can attack and damage Heavy Infantry.
Knights are very effective against the Trebucket. Their high movement speed allows Knights to easily reach Trebuckets and do massive damage. Meanwhile, Trebuckets struggle to do meaningful damage to Knights.
Knights were men who were granted knighthood after many years of training. They were generally born into nobility, and had to progress from page to squire before finally becoming eligible to becoming a knight at the age of 21. Knights in the Middle Ages wore full chain, and later plate armor. They were trained on horseback riding and a variety of weapons. Eventually, armored cavalry and knights were made obsolete with gunpowder weapons, where a soldier trained in weeks on a firearm could bring down a knight who spent years in training. However, the chivalrous code that knights followed still continues in some knighthoods to this day.