In the Middle Ages, approximately 1000 to 1400 AD, the weapon that dominated all land wars was a man, covered in various types of metal armor and armed with sword, spear, and axe, mounted on a horse that had to be large and strong enough to carry all that weight. This weapon was called a knight. The reign of the armored knight was broken partially by the English longbow but finally by the advent of guns for infantry soldiers. The Warrior Knights by Paul Williams describes, briefly and in general, what these knights were like and how they fought in the four centuries they dominated. It is a picture format book but with lots of detail and reading level more on the middle school or upper elementary level.
Two famous knights at that time, who were also kings, were known more for their knightly prowess than their kingly statesmanship. These were Robert the Bruce, eventually the Scottish king who won independence from their English masters, whose story is told in Outlaw King by Peter John Stephens. Richard I of England, the great-great grandson of William the Conqueror, was the most renowned knight of his day, known for his great strength and skill as a knight. Too bad he wasn’t all that wonderful as a king. Still, he is a great character in the Robin Hood stories. The Crusader King: Richard the Lionhearted by Richard Suskind tells King Richard’s story.
By the way, although there are no more mailed knights today, except for some reenacters, descendants of the horses still survive in some of the breeds of large horses we see around us, such as Percherons and Friesians. In case you wondered, apparently the Budweiser Clydesdales are a more modern breed and not descended from the horses of knights.