A slight alteration to the custom of riding a horse may have dramatically changed the way wars were fought. Humans rode bareback or mounted horses with a simple blanket after they first domesticated the animals, thousands of years after the dawn of agriculture. The leather saddle first straddled a horse’s back in China perhaps as far back as the third century B.C. But the saddle was only one step toward transforming the use of cavalry as a means of waging war. Climbing onto a horse while bearing weapons had long presented its own precarious hazards. Cambyses II, a Persian king in the sixth century B.C., died after stabbing himself as he vaulted onto a horse.

By the fourth century A.D., the Chinese had begun to fashion foot supports from cast iron or bronze. What made the stirrup (derived from the Old English word for a climbing rope) such an important innovation was that it allowed the rider immensely greater control in horsemanship: rider and animal became almost extensions of each other. It was possible to shoot arrows accurately while the horse dashed ahead at full gallop. A cavalryman could brace himself in the saddle and, with a lance positioned under his arm, use the tremendous force of the charging horse to strike a stunned enemy. The horse's sheer mass and quickness became an implement of the cavalry's weaponry—and a powerful intimidation factor.

The fierce Avar tribe may have brought stirrups to the West when it arrived in Byzantium in the sixth century A.D. The Byzantine Empire soon adopted the stirrup—and later the Franks embraced it as well. The societal impact of this saddle accoutrement has intrigued historians for decades. Some scholars suggested that feudalism emerged in Europe because mounted warfare, facilitated by the stirrup, became vastly more effective for the cavalry of the Franks. An aristocratic class emerged that received land for its service in the cavalry.

Others, on the opposite side of what is known as the Great Stirrup Controversy, argue that this interpretation of events is baseless. Whether the stirrups were the single enabling technology that brought about the rise of feudalism remains in doubt. Unquestionably, though, this small extension from a saddle was an innovation that transformed the craft of war forever.