The earliest modern “circi” were glorified riding demonstrations, single-ring answers to that most ancient of questions: What do you do with your soldiers in peacetime? In 1768, on the eve of what the British call the American War of Independence, Philip Astley and his fellow cavalrymen of the Fifteenth Light Dragoons opened an outdoor “riding school” at a track outside London. What made their presentation a circus, in the sense that we’d know it, was that it combined the displays of equestrian prowess—including trick-riding, jumping, and military maneuvers in the styles of the Prussians and Hessian hussars—with interludes of clowning that allowed the riders and horses to rest, and were thought to appeal to women and children. [...]