Piazza del Campo, Siena

Sloping like a giant scallop shell, Siena's Piazza del Campo was completed by 1349 as the civic heart of a fiercely independent medieval republic that rivalled Florence. Its nine converging paving segments recall the 'Government of Nine' that ruled Siena's golden age, when Ambrogio Lorenzetti frescoed the nearby Palazzo Pubblico with his 'Allegory of Good and Bad Government.' Twice each summer, on 2 July and 16 August, the square is ringed with earth for the Palio—a frenzied bareback horse race between the city's 17 contrade (districts) that lasts about 90 seconds and traces its roots to the 17th century. Passions run so high that alliances, betrayals, and centuries-old rivalries decide the outcome as much as the horses.