One positive thing about the Dark Ages was that horseback ‘barbarians’ invaded, pillaged, and burned using a new development that today we call stirrups–an innovation that revolutionized cavalry and greatly eased saddle-soreness.
Stirrups increased cavalry’s effectiveness against infantry and allowed for the creation of new heavy cavalry with lances. Horses could be ridden faster and for longer distances: the gallop is easier for the animal if its rider stands in stirrups, and stirrups make trotting much more pleasant.
People had ridden in saddles for over a thousand years without stirrups, and the intellectual tone of the era makes it likely people would have gone another thousand without the bracing illustration of an arrow-spewing nomad bearing down at a fast gallop. The device was quickly copied and by 600 AD were spreading throughout Europe.