Felipe Fernandez-Armesto: The accidental criminal

"No one truly knows a nation," said Nelson Mandela, "until one has been inside its gaols." Last week, after living in the USA for more than a year without understanding the country, I acquired - briefly - a gaolbird's authority. I can now share insights you can only get from being assaulted by the police and locked up for hours in the company of some of the most deprived and depraved dregs of the American underclass.

For someone like me - a mild-mannered, middle-aged professor of scholarly proclivities, blameless habits, and frail physique - it was shocking, traumatising and deeply educational. It all started on my first morning in Atlanta, Georgia, where I was attending the annual conference of the American Historical Association. Unwittingly, I crossed a street at what I later learnt was an unauthorised crossing. I had seen plenty of pedestrians precede me. There was no traffic in sight and no danger to me or anyone else.

Apparently, however, as I was later told, "jaywalking" is a criminal offence in the State of Georgia. But I had no idea I had done anything wrong.

A young man in a bomber jacket accosted me, claiming to be a policeman, but with no visible evidence of his status. We got locked in mutual misunderstanding, demanding each other's ID. I mistook the normal attitude of an Atlanta cop for arrogance, aggression and menace. He, I suppose, mistook the normal demeanour of an ageing and old-fashioned European intellectual for prevarication or provocation.

His behaviour baffled me even before he lost patience with me, kicked my legs from under me, knocked my glasses from my nose, wrestled me to the ground, and with the help of four or five other burly policemen who suddenly appeared on the scene, ripped my coat, scattered my books in the gutter, handcuffed me, and pinioned me painfully to the concrete.

I was bundled into a filthy paddy-wagon with some rather unsavoury-looking fellow-prisoners and spent eight hours in the degrading, frightening environment of the downtown detention centre, with no humiliation spared: mugshot, fingerprinting, intrusive search, medical examination, and the frustration of understanding nothing: neither why I was there, nor how I might get out.

Had I made it to my historical conference, I might have learnt about medieval pumpernickel-production or 17th-century star-gazing. Instead, I discovered a lot about contemporary America.

First, I learnt that the Atlanta police are barbaric, brutal, and out of control. The violence I experienced was the worst of my sheltered life. Muggers who attacked me once near my home in Oxford were considerably more gentle with me than the Atlanta cops. Many fellow historians at the conference, who met me after my release, had witnessed the incident and told me how horrific they found it. Even had I really been a criminal, it would not have been necessary to treat me with such ferocity, as I am very obviously a slight and feeble person. But Atlanta's streets are some of the meanest in the world, and policing them must be a brutalising way of life.

Once in gaol I discovered another, better side of Atlanta. The detention centre is weird - a kind of orderly pandemonium, a bedlam where madness is normal, so that nothing seems mad. It's windowless, filthy, and fetid, but strangely safe, insulated and unworldly: like Diogenes's barrel, a place of darkness conducive to thought - for there is nothing else to do in the longueurs between interrogations, examinations, and lectures from the sergeant in charge about the necessity of good behaviour.

Some raffish underworld characters befriended me, but so did the detention centre personnel.

In gaol, I saw none of the violence that typifies the streets. On the contrary, the staff treat everyone - including some of the most difficult, desperate, drunk, or drugged-out denizens of Atlanta's demi-monde - with impressive courtesy and professionalism. I began to suspect that some of the down-and-outs I shared space with had deliberately contrived to get arrested in order to escape from the streets into this peaceable world - swapping the arbitrary, dangerous jurisdiction of the cops for the humane and helpful supervision of the centre. Nelson Mandela, I think, was right to say that gaol is the best place to make judgements from because, "a nation should be judged not by how it treats its highest citizens, but its lowest." If Atlanta is representative, America, by that standard, comes out commendably well.

I then met the best of America when I appeared in court. Everyone, including the judge himself and the wonderful vice-president of the American Historical Association, who accompanied me to lend moral support, told me to get counsel to represent me. A lawyer I had consulted hurriedly that morning had advised me to sue the city. But I had no stomach for such a hostile and elaborate strategy. Instead, I watched Judge Jackson at work. He had 117 cases to try that day. He handled them with unfailing compassion, common sense and good humour.

I noticed that my charge as the judge read it - "failing to obey a police officer and obstructing the police" - did not match the semi-literate scrawl the accusing officer had scribbled on my citation: so I reckoned that, if necessary, I could get the charges dismissed on those grounds alone. Meanwhile, I simply appealed to the wisdom and mercy of the judge.

It only took him a few minutes to realise that I was the victim, not the culprit. The prosecutors withdrew the charges. The judge then proclaimed my freedom with kindly enthusiasm and detained me for nothing more grievous than a few minutes' chat about his reminiscences of the Old Bailey.

The first lesson is obvious. The city authorities of Atlanta need to re-educate their police. I can understand why some officers behave irrationally and unpredictably. Much of the downtown environment in their city is hideous - inoffensive to the eye only when shrouded by the often-prevailing fog. The sidewalks are thronged with beggars who can turn nasty at night. The crime rate is fearful.

The result is that the police are nervy, jumpy, short-fused, and lacking in restraint, patience or forbearance. But witnesses tell me that up to 10 officers took part in the assault on me. This is evidence not only of excessive zeal, but of seriously warped priorities. In a city notorious for rape, murder and mayhem the police should have better things to do than persecute jaywalkers or harry an impeccable, feeble foreigner.

Moreover, Atlanta depends on its convention trade. The way the conventions centre is designed is extremely practical. There is plenty of good, reasonably priced accommodation. But if Atlanta continues to accumulate a reputation for police frenzy and hostility to visitors, the economy will crumble.

At least, the police need to be told to exercise forbearance with outsiders - especially foreigners - who may not understand the peculiarities of local custom and law.

But, at the risk of projecting my own limited experience on to a screen so vast that the effect seems blurred, I see bigger issues at stake: issues for America; issues for the world. I found that in Atlanta the civilisation of the gaol and the courts contrasted with the savagery of the police and the streets. This is a typical American contrast. The executive arm of government tends to be dumb, insensitive, violent and dangerous. The judiciary is the citizen's vital guarantee of peace and liberty.

I became a sort of exemplar in miniature of a classic American dilemma: the "balance of the constitution", as Americans call it, between executive power and judicial oversight.

I have long known, as any reasonable person must, that the courts are the citizen's only protection against a rogue executive and rationally uncontrolled security forces.

Though my own misadventure was trivial and - in perspective - laughable, it resembles what is happening to the world in the era of George W Bush. The planet is policed by a violent, arbitrary, stupid, and dangerous force.

Within the USA, the courts struggle to maintain individual rights under the bludgeons of the "war on terror", defending Guantanamo victims and striving to curb the excesses of the system. We need global institutions of justice, and judges of Judge Jackson's level of humanity and wisdom, to help protect the world.

I feel happy and privileged to be able to live and work in the United States. On the whole, in my work as an historian, I have argued consistently that America has had a benign influence on the world. The growth of anti-Americanism fills me with despair, as I see ordinary, decent, generous Americans getting the blame abroad for the follies of the American government and the crudities of the American image.

I hope that if some good ensues from my horrific misfortune, it will include more future security from police misconduct for visitors in Atlanta, and more awareness in the world of some of the virtues - as well as some of the vices - of US life.