The two and half hour build up to Siena's famous horse race looks, to the visitor, like a display by the world's largest "living history" society. But Cosima Spender, behind the camera, knows that the Palio - the furious bareback horse race that draws thousands of British tourists to the Tuscan city twice every year (on July 2 and August 16) - is far darker, and more complex, than the slightly hokey parade that precedes it.