A Edited Verion of How The Stirrup Changed Our World, by Dan Derby
http://www.strangehorizons.com/2001/20010924/stirrup.shtml

Aside from the wheel, there are few inventions that have had the impact on history and culture as the stirrup.  Many people believe that it was responsible for the entire feudal system and no one will argue that the stirrup the single most important factor in the rise of the mounted knight as the dominant weapon of the medieval period.

The horse evolved in the Americas about 20 million years ago and migrated into Eurasia and populated the steppes.  It was used as a source of food long before it was ridden.  In the Americas, it was eaten into extinction by 5000 BC, not to be reintroduced until the Spaniards brought them over in the 18th century.

However, before the Americans has chowed down on their last horseburger, the Russians had domesticated horses and were raising them as a food source, and somewhere around 6000 BC someone may have actually ridden horses for the first time. 

As you can imagine, the first bareback rider didn't have much control.  Eventually, the bridal was added and the rider now had significant control over the animal.  Suddenly, man could cover distances in a few hours that used to take him days.  He had unknowingly created a new strategic weapon, the high-speed retreat.

You may wonder how a retreat becomes a weapon. The most dangerous part of warfare during those days was getting away.  Warfare was usually involved surprise hit and run tactics on superior forces.  The idea was to strike, inflict as much damage as possible, and get away before the enemy regrouped enough to push back the attack and inflict damage on the attackers.  The people of the steppes became skilled horsemen and dominated the area for the next few thousand years.

Around 1000 BC someone added a simple loop of leather to the saddle that allowed the less athletic rider to mount the horse easier.  From there it was simply a matter of time before someone added the loop to the other side and a new advantage was found.  The rider was now much more stable.  Before this simple invention, only highly skilled horsemen were able to ride and carry weapons with any effectiveness.  It took great skill and a great deal of practice.  Add this to the cost of raising horses and you found that horse warfare didn't come cheaply. 

Now with the invention of the stirrup, less skilled riders could become warriors and the horsemen of the steppes had an even greater advantage.  Their numbers rose and by 317 AD the horsemen of the steppes had overridden China.  The countless number of foot soldiers that China could produce was no match for the mounted warriors of the steppes.

With each new land conquered, the stirrup was introduced to a new culture and by 600 AD they had made their way to Europe.  The horse soldiers still depended on the hit and run tactics, but now did is with much greater numbers.  The European foot soldiers had great difficulty dealing with the mounted attacks.

By 700 AD Europe began to adapt by taking the best of the ideas of their enemies with their own ideas.  They began to develop a new form of society that produced a new type of warfare.  They built their society around the weapon system, the mounted knight. 

The horse warrior of the steppes road small swift steppe ponies, was clad in leather armor, and usually carried a bow and/or spear.  Imagine the first time they attacked a walled castle. Their excitement grew as the charged and watched the workers fleeing for the protection of the walls, but then quickly fades as they see coming out of the fortification the biggest horses they have ever seen and mounted on the horses were knights in metal armor carrying the biggest spear they had ever seen.

Suddenly, the steppe warriors practiced the rapid retreat developed by thier ancestors, but now it was before they attacked instead of after.  They had encountered the Sherman tank of the 8th century.  It was expensive was to raise horses and to become skilled at using weaponry while mounted, but the cost of maintaining mounted knights was staggering.  The entire feudal system evolved as a way of supporting this new type of warfare. 

All of this was made possible by the invention of the stirrup.  Without it, the steppe horse soldiers wouldn't have been able to dominate. Without it, the knight would never be able to stay in the saddle. Mounted knights were to dominate Europe for the next 600 years until other forms of defense and weaponry made the role of the knight unnecessary, but that's another story.