Originally, Franks campaigned on foot, but their armies evolved to become a cavalry force. As mentioned above, the appearance of the Eastern stirrup provided riders with a relatively stable fighting platform, to the point where the impression is strongly rooted that until the introduction of gunpowder, cavalry dominated the battlefield of the medieval era.
Cavalry played an important role on the battlefield and no, the medieval period was not without creative insights into weapons technology, quite the contrary. Certainly, the Middle Ages was frequently presented as a period of history when the relative absence of central authorities did not make it possible to gather the ideas and capital necessary for the evolution of armaments.
On the other hand, particularly in the context of major invasions and migratory outbreaks, the medieval period saw defensive action become a priority. The various castles and fortifications were designed to stop an opponent, but also to live there. Castles were naturally erected at places considered strategic, either in the heights or near watercourses. On the banks of tributaries, castles could easily be supplied with water, which could be vital for defenders during sieges. As for the walls, their height forced the attackers to use their imagination, both to climb them and to pierce them. If there was an "error" on the part of the attackers in the Middle Ages, it was perhaps in the lack of knowledge transfer in siege warfare over the centuries. Again, these are case-by-case and it would be unwise to generalize, although some of the ancient gains in siege warfare were temporarily lost in the Middle Ages.
On the other hand, the art of archery evolved in the Middle Ages and the crossbow became a weapon that significantly changed the situation on the battlefields, because it was now possible for a soldier on foot to shoot down a mounted opponent, a noble moreover. The short arrow of the crossbow could pierce the best mesh size. On this point, the use of the crossbow for warfare is one of the first cases in history where the Catholic Church tried to regularize its use, without much success. Moreover, this type of intervention by religious authorities did not stop the innovative enthusiasm for weapons.
Other weapons very effective for hunting were used for military purposes such as the longbow, a weapon particularly present on the battlefields during the Hundred Years' War. The longbow had a fast firing rate as well as a long-range. There is a first proven case of its use during the Battle of Falkirk in 1298, where it was used to provide offensive support fire to the cavalry. During the Cens Ans War, and more particularly in Crecy (1346) and Azincourt (1415), the French knights were the victims of a hellish shooting of thousands of arrows raining from the sky and projected by well-trained and disciplined English archers.
The other element that began to discourage any horseman from advancing towards the enemy at full speed was the introduction of the spade, which was, in fact, an improvement of old weapons. The spade was a combination of spear, hook, and ax that allowed the infantryman to hook the enemy rider, knocking him off his horse, then disperse him or even pierce his armor once the attacker was on the ground. As the Swiss demonstrated at the time, a well-disciplined infantry formation could stop an aggressive cavalry charge.
It was also during the medieval period that gunpowder was on the horizon. Invented by the Chinese before the 13th century, gunpowder was probably first used in the war during the Battle of Crecy mentioned above. In the long run, its use forced strategists to review their tactics, but questions began to arise about the relevance of building and maintaining castles and fortifications. The first constructions emphasized the high structures, although, with gunpowder, they would now be much lower, a little more discreet in the landscape and thicker to better withstand the impact of penetrating bullets. The classic case of the first major fortification under artillery fire is the fall of Constantinople in 1453. Having been able to stop invasions for centuries, the walls of Constantinople collapsed, this time under Turkish artillery fire.
But, not only did we have to improve the metallurgical components, but we also had to consider designing sighting systems and improving the composition of the gunpowder of the time, which was often far from perfect. Despite its shortcomings, gunpowder, much like the crossbow and longbow, allowed the foot soldier to own a firearm and shoot down a mounted enemy. Here again, knighthood mounted by elites would again become vulnerable to infantrymen equipped with firearms whose training no longer required as much time and financial and technical resources.