When Hunter S. Thompson took the English artist Ralph Steadman to the Kentucky Derby in 1970, he tried to prepare him for the chaos into which they were descending. “Just pretend you’re visiting a huge outdoor loony bin,” Thompson said. He added, because he was rarely out of character, “If the inmates get out of control we’ll soak them down with Mace.”

“Huge outdoor loony bin” is not the most precise description of the Palio di Siena, the thunderous, lawless, bareback, medieval-style horse race held twice each summer in front of tens of thousands of spectators on a track of packed clay laid down in the downtown heart of Siena, in Tuscany. But it will do for the moment.