Muhammad Ali and Cleveland Williams boxing at the Astrodome in Houston, Texas in 1966. Photo / Getty Images
The photograph is taken from high in the roof of the arena, directly above the action. It shows the white square of a boxing ring and the first few rows of seats around it.
These seats are occupied by journalists and photographers who have little desks in front of them for their cameras and portable typewriters.
You can't see the vast crowd behind them, but you can sense it, the thousands of seats all turned towards the nub of the arena, the single point of focus, the ring.
Inside the ring are three people: two boxers and a referee. The boxers are black, the referee white. One boxer is withdrawing to the corner. The other is flat on his back.
Not even a knee is off the canvas. His arms are raised beside his head as if surrendering to the police. He is obviously unconscious. He could as easily be dead. The referee is counting him out.
The photograph was taken half a century ago in the Astrodome in Houston, Texas. Effectively it could have been taken 20 centuries ago in the Colosseum.
Here were all but naked athletes from a social underclass, fighting until one of them falls, and doing so for the entertainment of the overclass, the full-clothed and baying citizens.
We like to think today that we've evolved beyond the cruelties of the Colosseum, and we do indeed recoil from the idea of pitting men against wild animals - though mainly, it should be said, out of sympathy for the animals. But we remain as fond as the Romans were of watching other people fight.
The Colosseum was a place of entertainment, the Roman equivalent of Hollywood. And Hollywood delivers quantities of death and maiming that the Colosseum's boss could only dream of.
By the time he's 10 the average child today has witnessed 50,000 murders on television and committed six times that number in video games.
I made those figures up but I've no doubt that they are underestimates. And adults are just 10-year-olds in long trousers, their taste for violence undiminished. Tarantino wins awards for gratifying it.
Like the Romans, we adore our gore. Much of what we see may be simulated, and thus easier on the conscience, but the taste is as unequivocally there as it was in Nero's day.
And we still like the actual violence too. Cage fighting is a recent innovation. It makes boxing look genteel. Its only rule is that there are no rules.
The Romans would have loved it. And just as 2000 years ago it's still the underclass, the less favoured races, that fight for our amusement.
The prostrate boxer in the photograph was Cleveland Williams. Two years before the photo was taken he was stopped by a white police officer for speeding.
According to the official report he resisted arrest and in the ensuing struggle the policeman's gun went off accidentally.
Williams underwent four operations over the next seven months. He lost a kidney and 10 feet of small intestine. When he recovered he was fined $50 and jailed.
The other boxer was Muhammed Ali. Until shortly before then he'd been Cassius Clay. That name was perfect: Cassius evoked classical statuary; Clay evoked flesh.
As John Curry did with ice-skating, and David Gower did with batting, Clay turned a physical craft into a visual art. He was not only lovely to look at, his face unscarred and almost babyish, but he made punching and avoiding punches beautiful. He danced amid danger.
I didn't see the fight with Cleveland Williams. But I did see him fight three years earlier in 1963 when he came to Britain to take on the local champion Henry Cooper. I was 6 years old. I remember it vividly.
My whole family sat round our little black and white television to watch. The ringside seats were occupied by rich old men in dinner jackets and bow ties.
Cooper was a working class lad from South London with accent to match. He had a famous left hook and he knew no fear. But it was Clay you couldn't take your eyes off.
He boxed on his toes and he spat out his jabs and though Cooper famously knocked him down he jabbed Cooper's eyebrow to a pulp, a jellied mess, a butcher's window, till Cooper couldn't see for blood and the fight was stopped.
And the announcer climbed into the ring, also in a dinner jacket, and he stood beside these two bloodied and almost naked men and announced the winner and the referee held Clay's arm aloft and this little Roman loved it.