The Palio di Siena horse race takes place twice a year, in July and August, in the central piazza of the Italian city.
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Thousands swarm to the venue to watch riders from each of the districts battle it out for race glory in front of their fellow citizens.
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All the riders wear the respective colors of their districts but, in a race dubbed by some "the toughest horse race in the world," they must ride bareback.
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Glorious sun shone on the crowds for this year's opening event on July 2. The race is said to date back to medieval times.
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Jockeys can use whips not only on their own horse, but also to disrupt a rival horse.
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The winner is the first across the line but, unlike traditional horse racing, victory can be sealed even if the horse has unseated its rider during the course of the race.
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A supporter of the district (or contrade) of Lupa cheers on his horse during the July 2 running of the event.
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Animal rights protesters, complaining that seven horses have died on the course since 2000, have tried to get the event abandoned.