Immensely important innovation that allowed the dominance of cavalry on the battlefields of Asia and Europe for centuries.

Only the practical application of gunpowder for use by infantry superceded it.

This is one of the more important inventions in the world. The stirrup was invented in the East someplace, but did not get to Europe until about 600 A.D. Hugh Thomas has a great book, "History of the World," that describes the development of all the common tools and devices, and I will have to look up where the stirrup was invented.

The stirrup lead to the rise of heavy cavalry who could fight in the saddle. Imagine riding a horse, wielding a spear, and ramming the spear into an en enemy. Without a stirrup, the rider could well become unhorsed. With the stirrup, he can triumph and remain in the saddle.

After the invention of the stirrup, cavalry ruled warfare for the next 1000 years or so until gunpowder changed the equation.

The stirrup allowed Charles Martel to defeat the invading Mohammedans at the Battle of Tours in 732 and saved Europe.

In warfare, stirrups changed everything. Before saddles (without stirrups), chariots and gunpowder, they ruled on the battlefield. They gave the rider stability and, thus, an advantage in power and maneuverability when using weapons. An army that was outfitted with stirrups made their enemies look like drunken wheel chair retards...

Well it's still possible to ride horses without these, so maybe they're not that important

OOOPS! My thoughts were dirty!

I like the Star Wars reference and it sure is accurate...

The most important invention that nobody knows about. No one even knows who invented it, though its impact was revolutionary. The stirrup made it possible for a man to shoot with a bow and arrow from a horse, without stopping, or easily strike with a sword/mace/lance without losing his balance. The barbarian invasions that plagued civilized (agrarian) people from around 300 AD to 1500 AD were due the stirrup; before then, disciplined infantry could usually defeat cavalry. The stirrup turned cavalry from a marginal auxiliary (mostly 'mounted/mobile infantry') into the most important part of any military force. The centralized empires of the ancient world crumbled, and feudalism spread across Eurasia, largely due to the stirrup. It also gave nomads a huge military advantage over agrarian/urban people; an advantage that would last until the invention of gunpowder.