Armed with crossbows, however, ordinary farmers could shoot down the best-trained, best-armed knights of the day. Suddenly, sitting astride a horse was a problem, rather than a tactical advantage, because mounted knights made easy targets. Bolts fired up at them could slip beneath armor plates—into the armpits, for example—and direct hits penetrated regardless. Horses could be toppled, too, bringing the mass of muscle and metal crashing to the ground so that a knight lay underfoot, as helpless as an overturned turtle.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 426