Since before the spear, warfare has always stimulated technology. Assyrian military

engineers, Macedonian weapons inventors, and Roman fortification builders were the

weapons techies of their respective times.

It’s hard to imagine anybody coming up with a horrific substance such as Greek fire, a

highly combustible liquid that long predated twentieth-century napalm, if not to use it

as a weapon. And metalworking seems to have fed on the needs of weapons makers

and armorers. But inventions spur warfare, too.

More than a millennium ago, two dandy little innovations from Asia enabled and

demanded many adjustments in how wars were fought and even how war was

perceived. These innovations were

Gunpowder: The Chinese mixed up the first batch in the ninth century AD,

although they didn’t try to blow anybody up with it until a while later.

The stirrup: Far less flashy than gunpowder but exceedingly practical, the low-

tech stirrup — that thing that you put your foot into to climb onto and ride a

horse — became part of a Chinese horse soldier’s gear in the fourth century AD.