This is a wide topic, I admit, but I try to be as brief as I can.

The medieval era from the fall of western Rome to the rise of renneissance was the era of the heavy cavalry in Europe. The Roman legion was made obsolete by more mobile and better equipped heavy catapracht cavalry, that the Romans adopted from their eastern neighbours in Armenia, Syria, Persia and the Scythians, Sarmatians and the Huns of the wide steppe. The medieval epitome of warfare was the concept of the Knight. Armoured, highly skilled and armed like his predecessor the cataphract with a lance and sword.  A knightly culture and social class ruled over rest of the society for some thousand years and went into decline as the infantryman once again surplanted the heavy cavalry as the foremost element to win any battle.

So highly was the heavy cavalryman regarded in medieval times, that often even though armies consisted from far more greater numbers of infantry (of varying quality) their numbers were not even mentioned or really counted when the strength of an army was evaluated. Examples of this can be found from the opposite ends of the European continent. Even in the long tradition of military training and analysis of the Byzantine empire they would often only count the number of cavalrymen, when they made estimations of their campaign forces. When the English met the French in the battle of Azincourt in 1415, the contemporary sources say that the French outnumbered the English three to one, but in reality this only meant that there were three times the amount of French chevalliers and gendarmes in comparrison to some 1000 English knights and men-at-arms. We know, that there were several thousand English archers and siege specialists on the field as well, but we simply do not have any contemporary estimate as to how many infantrymen (crosbowmen and such) did the French bring. Neither the archers or the crossbowmen, nor any of the possible billmen, spearmen, halbardier, or what ever were expected to have any impact on the result of the battle.

One might think that such disregard of the infantry was the result of mere arrogance coming from a sort of espirit de corps -sort of elitist social culture. In part it was that, and as in Azincourt, sometimes this sort of arrogance was proven to be fatal, but there were reasonable reasons for this attitude. The archers and crossbowmen and what have you other sorts of infantrymen were brought to field battles only to give a supporting role to the “real” soldiers of the heavy cavalry. Their main function was to serve as siege troops. To provide the necessary arrow fodder and shoot their arrows to make both assaults on ramparts and their defence difficult, but not to solve any field battles or even sieges. Thre were battles fought where a score of few hundred heavy cavalry destroyed several times stronger armies of infantry, suffering hardly any losses in turn. In comparrison the individual infantryman, hired or levied, had rudimentary education to the arts of close combat, was poorly equipped and motivated. The armoured man-at-arms in effect ruled the battlefield wether if he was mounted, dismounted or stood on the parapet of a castle.

The military ability of the man-at-arms did not only provide possibility for him to set himself to lead the society, it was also seen as a justification for him to stand in that position. The relevance of the knightly class in the medieval society has often been misunderstood and not seen as significant as it was, because such institutions as the church painted a bit different picture and gave other excuses for those who held power than their ability for violence and quite a bit of the contemporary sources from said era were written and preserved to posterity by the priesthood. But the medieval era was far from being extremely religious. It was superstitious and religion gave plenty of moralist excuses for the violence, but this was because the priests almost invariably came from the same social class as the men-at-arms. The priests were born as sons of knights, lords and well, other priests. Medieval bishops often had themselves depicted in armour, rather than in religious vestments. In general it seems religions do not set the moral standards for any society, rather the society sets the moral standards for the religion they have adopted. For the medieval European Christians church was not much else but a method to justify the feodalist social system, just like for the modern US Christian fundamentalists their churches are mere methods to justify their Capitalist values.

This dude in the picture is the archibishop of Cologne from around mid 14th century. His shield has the cross emblem, not uncommon heraldic device for less religious troop types either, and his helmet bears the bishops mitre as a heraldic device from wich his status can be easily recognized on the field of battle.

It has been often presented, that the introduction of gunpowder made the heavy cavalry obsolete, and thus ended the era of the knights. But this is a silly notion, as we know that the heavy cavalry retained it’s elite status on the battlefield even long after Napoleon. There are several reasons why heavy cavalry went into decline and foremost of them is that they themselves started to dismount for combat more and more often during the late medieval centuries.

The warhorse was an expensive asset to loose in combat, so it stood to reason not to waste it in so many frontal charges. While the benefit of the cavalry is the hard hitting mobility, this mobility makes it also an unreliable battlefield asset. If the heavy cavalry decides to retreat, they do it faster than any infantry, and that is one of the main reasons why medieval infantry was considered weak and unreliable, as they had to run away from the field long before their mounted masters decided to, if they did not want to be the ones easily cut down in the chase by enemy heavy cavalry. In the late medieval times some military minds gathered, that infantry could be a lot stronger, if it was armed so that it could withstand enemy cavalry charges on it’s own, without the support of the men-at-arms wether mounted or dismounted. Great national armies began to appear as kings and cantons were no longer dependable on the feodalistic protection racket. With the appearance of the national armies and autocracy slowly the national states appeared as well. And thus the medieval social structure based on the monopoly of violence by the heavy cavalryman crumbled. This in turn released all sorts of new ideas, that led to religious reformation, but more importantly to ideals of human value and enlightenment.

Sadly the history of warfare is not just a straight line of violence and of technological innovation separate from the rest of human achievement, but rather the history of human sociological evolution.