My old Palio - Siena's spectacle is more than just a horse race

The first raindrops fell on the square in Siena shortly before 6pm and it was sweet relief after a day baking in 33c sunshine. But as the sand and clay track started to spatter, the 60,000-odd people packed inside the temporary perimeter grew nervous.

Some had already spent three or four hours in the Piazza del Campo, patiently guarding spots close to the fence for the best view of the one-kilometre bareback horse race known as the Palio di Siena.

A collective groan went up at the emergence of the dreaded green flag on the Palazzo Pubblico (Town Hall). No race today.

The Palio is far more than just a horse race though. It is heritage. It is pageantry. It is local pride.

The Sienese obsession takes place twice a year, on 2 July and 16 August, both of which are Catholic feast days associated with the Virgin Mary.

It is contested by the medieval city's 17 contrade (districts), which started out as military catchment areas and profession-specific wards when Siena was a republic but are now neighbourhood societies centred around a church and hall. They used to compete against each other in everything from team boxing to bull-fighting until settling on horse racing in 1633.

Each contrada has its own unique colours, motto and symbol, often an animal. There are alliances and fierce rivalries, with noisy neighbours or a crowd that blaggarded yours at some point over the last 391 years. It's all a bit Harry Potter. But you wouldn't say that to their face.

The emblems of the contrade

As you walk the streets of Siena in a straight line from the northern gate of Porta Camollia, the decorated lamp-posts and flags signal the flow of borders, Istrice (Crested Porcupine) giving way to bitter enemies Lupa (She-Wolf), then Bruco (Caterpillar),