The Ashes are under way in England, but another historic sporting battle is fought out every year in Florence - an ancient no-holds-barred ball game played in one of the city's most famous piazzas, as writer Sarah Dunant explains.

Britain is a happy nation this week. The sun has shone and we've won a major sporting tournament.

I say we, because although obviously our new national hero did the physically gruelling bit, we've had our own work-out too. Tennis - like cricket, football, athletics, etc - may be a game, but it's only a sport when you have spectators to amplify the contest. Pumping the energy, riding the adrenaline spikes, aggression, exhilaration, outrage, even the occasional increased heart rate as we leap up from our sofa.

At the end, triumph or failure. With luck and without immediate access to too much alcohol, both sides can enjoy the catharsis of all emotion spent. Thus in theory, throughout history, sport has proved a creative alternative to our recurring tendency to kill each other.

Which brings me to Florence, where I work part of the year and where we're also recovering from annual sporting therapy, in this case a much less gentlemanly ball game that takes place in a giant sandpit in the middle of the city.

No one knows exactly when "Calcio Storico" - historic football - was first played here, but its pitch, the piazza of Santa Croce, dates from the 14th Century and the rules of the game - in so far as there are any - were written down in the late 1500s. The four quarters of the city - Santa Spiritu, San Giovanni, Santa Maria Novella and Santa Croce, named for their great local churches - each put up a team of 27 men.

The aim, over two heats and a final, is for players to get the ball over the 4ft (1.2m) fence at either end of the pitch. To achieve this, players can use both hands and feet, as well as every other part of the body when it comes to wrestling, punching and generally immobilising their opponents on the way. In other words - sport as muted warfare.

A 15th Century Florentine would still recognise much of the event. Each game is preceded by trumpet fanfares and marching drums as costumed dignitaries and flag-throwers in the rich hot renaissance colours of their teams march from their various quarters to the piazza. The only concession to sartorial modernity - the players' coloured t-shirts with sponsors' logos - are off within minutes of getting onto the pitch, so that all one can see is naked upper torsos, caked with sand and sweat, hurling themselves at each other, as the crowd roars its approval and each goal, or caccia, is greeted by cannon fire.

The addition of tourism has done little to blunt the edge of civic competition and not-so-benign thuggery that comes with it. Time travel works both ways, and watching from my window as the teams arrive (in the Renaissance most respectable women wouldn't have been allowed out anyway), you get a distinct whiff of a darker, more physical past, where the streets were often full of excess testosterone looking for action.

Image caption Calcio Storico takes place in the Santa Croce Piazza, Florence

Italian Renaissance city-states were tiny affairs compared to modern conurbations, but rivalries between prominent families and gang warfare (think Verona and the Capulets and Montagues) were always simmering under the surface. Smarter authorities found civic ways to let off steam.

Throughout history sport has proved a creative alternative to our recurring tendency to kill each other

There was Siena and its Palio - different quarters of the city slugging it out on a death-track horse race. And Venice for centuries had a spectacularly violent sport of bridge fighting. Imagine this as your local sporting fixture - on big public holidays (of which there were many), a battalion of fishermen would meet an equal number of pumped-up ship workers at a pre-arranged bridge - there is one still known as Ponte dei Pugni ("bridge of fists") - and, armed with sticks and staves tipped in boiling oil, beat the hell out of each other until, by falling back or into the water, one side was vanquished and the bridge was taken.

There were injuries and deaths but there were also stars - a number of Beckhams and Bests, though I am sure less good looking - who became local celebrities. There were also the corporate or royal boxes where the ruling families and visiting dignitaries could get a superior view of the action from specially constructed rafts moored nearby. In 1574 Henry III of France visited Venice and attended one such fight put on in his honour. His verdict: "Too small to be a real war and too cruel to be a game."

Horse-racing through winding streets, bridge fights in a city of water - while today we spend millions on sports stadiums (as much a way to control the crowds as the sport), they used what they already had. But then, one of the great things about Renaissance culture is that early on, it perfected an ideal architectural form which encouraged both containment and celebration - the piazza or city square. And they don't come any more heavily used than that football pitch in Florence.

The Franciscans who built the great church of Santa Croce, which dominates the piazza, picked the area because it was poor. Close to the river, this was where the dyers lived. Here, from great vats of scalding water, Florence's mercantile fortune emerged. Raw dull fabric was imported from all over Europe and turned into rainbow colours to feed the appetite of growing fashionable middle classes. Walk into any church and you see the results pulsating off the walls: frescoes telling biblical stories but set in contemporary 15th Century, the background figures often local citizens dressed to the nines.

But if the original inhabitants of Santa Croce didn't share in the wealth, they did enjoy some of the spectacle. It was in their piazza that the Medici family celebrated the wedding of Lorenzo (soon to be the Magnificent) with a tournament. They also had prime access to one of the great preachers of the age, San Bernardino, whose hellfire sermons were so compelling that the congregation spilt out of the cavernous church to fill the great space outside.

In recent years there have been modern prophets. Since they moved the 19th Century marble statue of Dante from the middle of the piazza to its current position on the steps of the church, the piazza has become the perfect venue for outdoor rock concerts. Here, during a balmy September night four years ago, I had my own form of epiphany, enthralled by the musical sermons of Leonard Cohen. I remember wondering then what Dante would have made of it all, though the real challenge to his famously disapproving marble features was last year when the Italian actor Roberto Benigni came to Santa Croce for his famous recitation of cantos from the Inferno. He returns next week for the final circles of hell to an expected audience of 60,000 a night.

Of course the square has seen disaster as well as wonders. Despite irregular flooding, nothing prepared Florence for the night in November 1966 when the Arno broke its banks and the black waters engulfed the state archives and the great church, reaching as high as the Cimabue crucifix hanging in the nave. It was a national disaster, which in turn spurred an international rescue effort. Thousands of volunteers came from all over the world to help in the clean-up operation.

But in the end, as with all great civic spaces, it's the piazza's everyday existence that gives it power. Though Santa Croce may be richer these days, it is still full of little apartments, many with limited access to light or outside space. The piazza is our public playground. Early morning dog-walkers, children on scooters and bikes, the occasional market, the hordes of tourists and the buskers, painters and the souvenir sellers who swarm around them.

The best time of day is the early evening when the sunset watchers gather on the steps of the church. Many are American students looking forward to an evening's bar crawl, something their age would deny them back home. My favourites are the Paris Hilton lookalikes, who totter across the flagstones on vertiginous heels that would have been a challenge to the stilts worn by Venetian courtesans 500 years ago. Commerce, concerts, sport and the endless theatre of people watching - Santa Croce has it all.

Image caption People have always come to the piazza to show off the latest fashions

Talking of sport, I bet you'd like to know the result of this year's Calcio Storico. It was dramatic stuff. The final, usually played on 24 June, the feast day of St John, had to be cancelled due to torrential rains. In true Calcio spirit the blues and the whites were actually inside the sodden sand pit vigorously disagreeing about whether or not to play, when it was officially stopped for safety reasons.

When it took place six days later, the winners were - yes! - the blues from Santa Croce. It was clearly a cathartic encounter - a fifth of the players were sent off for violent behaviour - and the celebrations that followed were, well, full-blooded. I know this because I was awake most of the night listening to them. That's another thing that hasn't changed in Florence. Those pavement stones echo as much in the present as they did in the past.

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