From China to the former Soviet Union, the history of the former Communist bloc is being rewritten - its achievements, mythical or real, discredited in the cold light of the post-Cold War: Beijing still claims to be `socialist' but has done its own demolition job on the revolution; in the West, wildly exaggerated tales about Mao Zedong's private life have surfaced ahead of the 100th anniversary of his birth. More accurately, the starvation of the Great Leap Forward and the suffering of the Cultural Revolution is now fully acknowledged. But one secret skeleton has remained hidden until now.

Earlier this year a dissident Chinese writer published the claim that people had not only been killed but eaten in south-west China during the Cultural Revolution. Could this really be true or was it just another piece of back-street gossip? Abroad, former `friends of China' were particularly upset. So many of their illusions about the Mao era had already been shattered: this was one revelation too far.

The only one way to be absolutely sure was to visit the town of Wuxuan in the south-western province (technically an `autonomous region') of Guangxi where the worst cases had allegedly occurred. Beneath the covered market in Wuxuan's main square, sacks of rice and bundles of tobacco were being traded in an early-morning grey mist. The subject of cannibalism is not an easy one to raise, even twenty-five years on, in a country where history is entangled with politics. But within half an hour, I had secured an unambiguous answer.

`Yes, the killings were really bad in Wuxuan,' said Mr Li, a friendly middle-aged local government clerk. `Just over there' - he pointed towards the old town - `I saw them rushing down. Then there was a big explosion, right next to the market, and bodies everywhere!'

But were people really eaten was well? `Of course they were; it's absolutely true, not false at all! And in Wuxuan,' Mr Li added with a touch of pride, `we ate more people than anywhere else in China!' Lii is not his real name, although he wrote it down readily with his address in my notebook.

His cheerful confirmation was both depressing and enlightening. Suddenly everything around me began to make historical sense. Old Wuxuan has hardly changed in the last quarter of a century and many of its walls still carry the faded slogans of the Cultural Revolution. The market square lies on its eastern side, the broad Qian River to its west. The town's main street runs between the two, descending to the water's edge in a flight of flagstone stairs. Most of the killings in May-July 1968 followed the logic of this simple geography. The market was where the victims were put on show; the river was the scene of the worst butchery. On the streets in between, these `class enemies' were paraded, hands and feet lashed with electric wire, forced to kneel and confess their crimes.

The fast-flowing Qian river rises near the Vietnam border, loops through Guangxi province and eventually - 500 kilometres downstream from Wuxuan - debouches not far from Hong Kong. These days it carries small smoky freighters, river steamers with narrow bunks for human sardines, and tiny barges towing enormous rafts of timber. At the height of the Cultural Revolution, it carried bodies.

The Hong Kong police fished dozens of corpses out of the harbour in the summer of 1968. There had been reports of fearsome fighting between Red Guard factions in Guangxi, and even Mao Zedong was said to have expressed alarm. But Wuxuan was too distant for its worst horrors to become known.

Some large, flat rocks near the water's edge were Wuxuan's killing stones. They made a convenient butcher's table for human dissection, and the unwanted bits could be disposed of easily in the river. Two typical cases are quoted in the official (but secret) chronicle of events which the dissident Zheng Yi obtained:

In the first, Zhou Shian was dragged to the town crossroads by a barber called Niu Huoshou and forced to kneel down. Beaten half to death, he was pulled down the long flight of stone steps to the riverside. Wang Chunrong then used a five-inch knife to cut Zhou open and extract his heart and liver. Others joined in and soon stripped him to the bone. Then they used a wooden boat to dump his remains in the river.

In the second, a raiding party from across the river seized three brothers from the Li family, and dragged them to the vegetable market where they were knifed to death. Their bodies were then carried down to the river, where the gang removed their livers and cut off their penises. The bodies were thrown into the river. That night they raped one of the widows, killed her pig and held a feast to celebrate the `great victory of the people's proletarian dictatorship'.

The secret report, compiled with bureaucratic thoroughness, also lists the `different forms of eating human flesh'. These included: `Killing and then having a feast, cutting up together but eating separately, baking human liver to make medicine, etc.' And it catalogues the `eleven different ways in which people were killed'. These were: `Beating to death, drowning, shooting, stabbing, chopping to death, dragging to death, cutting up alive, squashing to death, forcing someone to hang himself, killing the parent and raping the daughter, raiding to kill.'

These documents were the result of secret Communist Party investigations finally carried out fifteen years after the events. Most of those involved were punished, but with relatively light sentences: loss of party membership and/or jail terms of between one and fourteen years. When Zheng Yi visited Wuxuan (and four other Guangxi counties where cannibalism had occurred) in 1986 he was warned not to go out at night. Some of the killers still had powerful local connections.

After the Beijing massacre, Zheng and his wife, Bei Ming, went into hiding. Last year they escaped via Hong Kong to the US where he now works on Princeton University's China Project. Zheng is determined to the point of obsession to make the tale known and has just published Red Monument, a 700-page book, in Taiwan. The New York Times carried a report on Zheng in March this year (excerpted in the Guardian) and the dissident journalist Liu Binyan wrote a powerful article in the New York Review of Books. But reaction has generally been muted, especially among the overseas Chinese. Cannibalism is a distasteful subject and it reflects badly on the motherland. Why rake up the past?

Wuxuan County, with its population of 300,000, is tucked into the western folds of the grey and misty Great Yao Mountains in central Guangxi. It grows rice, vegetable oil, tobacco and sugar cane, but crop yields and incomes are much lower than the provincial average. Rural industry employs less than two per cent of the working population.

Wuxuan has always been `backward' in Chinese terms, and is only just beginning to be touched by Deng Xiaoping's consumer revolution. I arrived by boat from the lively port of Guiping in a five-hour journey which only passed one or two small villages. The scenery, almost as beautiful as that of the famous Li River near Guilin, is little-known to foreign or even Chinese tourists.

There were no street lights in Wuxuan's main square: a single food stall served oily noodles in the dark. I heard before I saw the large sow rooting through piles of rubbish on the broken pavement. Rats ran down the outer wall of a cinema showing an old kung fu film. I bought a stale moon cake and some chocolate in the dingy department store before it closed its shutters, but soon abandoned them to the pigs. In Guiping there had been shops with neon lights selling video recorders; cheerful street stalls with bright displays of fresh fruit; and an evening parade of teenagers in Hong Kong-style clothes. Here it seemed like China of ten years or more ago.

Yet there are a few splashes of light in Wuxuan's darkness. At the new end of town, along the modern highway past Party headquarters, cultural palace and government guest house, the first scouts of Mr Deng's revolution have arrived. These are the hairdressers and karaoke bar operators (often using the same premises). A young entrepreneur from the city of Liuzhou, newly established in Wuxuan, asked me to approve his window display of fashion posters and cut-out Chinese characters. But he complained of the high rent (500 yuan or fifty pounds a month) and the poor business. Too many people still have their hair cut in the market with a mirror hung against the wall.

The karaoke bars in Wuxuan are simple affairs, without giant screens or strobe lighting. A few tables are crammed into a small shop serving beer and peanuts: the screen is an ordinary TV set, but it has the latest videos. I stood on the mud-smeared pavement, watching a well-shaped young lady in one-piece bathing suit (no bikinis yet) floating on a surfboard somewhere in the South China Sea. `My heart leaps in the honey-sweet moon,' she mouthed, `I want to whisper that I love you. . .'

On the ground, the Great Leap Forward from cannibalism to karaoke is the distance between old and new Wuxuan, from the harbour steps to the new highway. Culturally, it is the distance from a society sealed from outside influence to one where every teenager knows who scored the goals in the European Cup. Those of the same age in 1968 were `revolutionary youth', rank-and-file fighters in the Red Guard struggles. Dozens of them died in the fierce battle which led to Wuxuan's summer months of slaughter. The children of those who are still alive will be the next generation of karaoke fans.

Not only Wuxuan but the whole of Guangxi province had been torn by political struggle for over a year (1967-68) between rival Red Guard factions each claiming to defend Chairman Mao to the death. These were manipulated by political cliques in the provincial capital and, through them, from Beijing. After a lull early in 1968, the more radical groups - known as the Small Faction because of their numerical weakness - were stirred up by signals from the `ultra-left' (Madame Mao and her `gang' in Beijing) to a last-ditch struggle. The Large Faction, controlled by Guangxi governor and army boss Wei Guoqing, then moved in literally for the kill. All Communist Party officials, right down to the village level, were ordered to `wage a Force 12 typhoon against the class enemy' and to carry out a `merciless class struggle'. The official (and minimum) estimate is that 90,000 throughout Guangxi died in what are now termed `unnatural deaths'.

On 4 May 1968, the Small Faction in Wuxuan had seized the harbour office and requisitioned its funds. In confused skirmishes a Large Faction leader was shot dead. The Large Faction called for reinforcements from two neighbouring counties and on the night of 12 May captured the Small Faction's base. The survivors, mostly teenagers, fled to a rocky outcrop in the harbour where they were rounded up early the next morning. At least thirty were killed on the spot.

At a memorial meeting for the dead of the Large Faction, two prisoners both students) were hung on trees as a `sacrifice' and butchered. They were the first to be eaten. Their hearts and liver were removed, cooked with pork and eaten communally. The head and feet of the Small Faction's leader, Zhou Weian, were displayed in the market place and his wife was forced to come and `identify' them. (Zhou Shian, whose slaughter is described above, was singled out because he was Weian's older brother.)

I shall only quote sparingly from the official account of the horrors which followed. Many school teachers were killed and at least two were eaten by their students. The headmaster of Tongling Middle School was the object of many struggle sessions. Although a guerrilla in the revolution, he had come from a landlord family. One night the students got tired of guarding him and killed him instead. The first person to eat his flesh was the girlfriend of his eldest son who had broken off the relationship.

A victim might be paraded and abused for some time before one or two individuals `dared' to kill him - watched with horrified fascination by the `masses', and by local officials who feared for their own lives. At first the victims were dragged to a secluded place before dismemberment, but within a month they were being openly butchered on the main street. The official record frequently notes in a chilling phrase that other people then `swarmed around to remove the flesh'. The most active killers were young men in their teens and twenties, including former members of the defeated Small Faction who sought to prove their new loyalty.

The taboo on eating human flesh was eroded by degrees. Zheng Yi suggests following sequence: (1) furtive eating by night, by individuals or families; (2) human and animal flesh are mixed together: those eating can delude themselves that they are `only eating pork'; (3) as the blood craze spreads, eating becomes a vogue. Different parts of the body are prized for their therapeutic value and cooked in a variety of ways. At the peak of the movement, human flesh is served at banquets with wine and loudly shouted guessing games.

The special horrors of Wuxuan finally became known in Beijing as the result of a remarkable act of courage which must have saved many lives. Wang Zujian was a former official - `upright' in the best Chinese tradition - who had been sent to a state farm in Wuxuan for criticizing Party policies in the late '50s. Released from the farm, he was now working quietly in the town's cultural office, hoping to keep out of trouble. Every day, as he walked to work, he was confronted by the slaughter on the streets. His wife, pregnant at the time, had arranged an abortion at the local hospital. She was so terrified that after two attempts to reach it she gave up. Wang resolved to denounce the cannibalism to the authorities, knowing that if his letter were intercepted he would probably get eaten too. He wrote to a relative, asking him to forward his letter to an old friend from the revolution, who in turn sent it to the capital. The ruse succeeded with dramatic results.

One morning early in July the rumour spread that a `big chief' was arriving to inspect Wuxuan. Soon a long convoy had arrived at the river port. Soldiers quickly fanned out to cover their commander as he entered the town. He was Ou Zhifu, commanding officer of the Guangxi Military District. Striding through the carnage, he confronted Wen Longsi, the head of Wuxuan's `revolutionary committee', and went straight to the point.

`How many people have you eaten here? Complaints have been made to Beijing! Why didn't you stop it? Why didn't you report it?' Pointing directly at Wen, he thumped the table. `Wen Longsi, from tomorrow, if one more person is eaten I'll make you pay. I'll blow your head off!'

The killing stopped immediately. Wen wished to save his head - so too did the Guangxi commander whose career would be blighted if Beijing blamed him for the `Force 12 typhoon'. The heroic Wang was identified after a friend revealed his name under torture. Wang was sent back to labour camp but not harmed. The town leaders feared subsequent investigation if they killed him too. His wife had the baby - their fourth child.

The eating of human flesh in Wuxuan and elsewhere in Guangxi had nothing do with the `famine cannibalism' recorded in China when millions have starved through war or natural disaster. It was `revenge cannibalism ' in which the victor demonstrates extreme contempt for the defeated foe by consuming parts of his body after (or sometimes before) death. Chinese dynastic history has recorded many such cases over several thousands of years. The philosopher Mengzi observed that `when men depart from righteousness and benevolence, they become like animals, even devouring their fellows'.

Not all cultures resort to cannibalism to take revenge on the vanquished. Western society prefers to humiliate the dead by mutilating and then displaying their remains. A typical modern example is the posed photograph of victorious soldier with severed head (US Marines in Vietnam, Indonesian rangers in East Timor, etc). Though any attempt to `explain' a society must be treated with great caution, the psycho-cultural view of China as an extremely `oral' culture seems to be relevant. Chinese attitudes towards food also suggest a therapeutic aspect. Bread soaked in the blood of an executed criminal was popularly believed to have powerful medicinal properties. A short story by the famous writer Lu Xun, Medicine, is based on this theme.

Cannibalism is a commonly used metaphor in China for the most destructive aspects of social behaviour. Lu Xun's most famous short story, A Madman's Diary, describing the patient`s delusion that he is threatened by people wanting to eat him, is a powerful allegory for the misrule of warlord China after the failure of the 1911 revolution. Similarly, a recent short story by a young contemporary writer, Wen Yuhong, describes an atmosphere of mounting blood lust which a witness to the events in Wuxuan would have readily recognized. In Wen's Mad City, a pair of ferocious butchers set a new fashion in slaughtering dogs for food. Everyone starts doing it too. Then one day they butcher a young man, and . . .

Can we be completely sure that the Wuxuan tale is not also fiction? Ever since the Conquistadores first traduced the Aztecs, Professor P. Arens has argued in The Man-eating Myth, Western societies have used the slur of cannibalism to de-humanize those whom they conquer, especially in the so-called Dark Continent. But apart from the Wuxuan documents and eyewitness accounts, there is substantial evidence of cannibalism in China in the past.

The distinguished anthropologist Wolfram Eberhard has identified five types of cannibalism including acts committed in revenge and for medical reasons. The majority of examples are found in south China among those ethnic groups known as `national minorities'.

Wuxuan's own population is 60 per cent `Zhuang' and the nearest county to the east is a `Yao' minority area. This offers a comforting alibi to friends in Beijing who can argue that what happened in 1968 was not really `Chinese' at all. In fact, most Zhuang have lost their original language and have been sinified by the dominant `Han' Chinese culture. But there is certainly an element of geographical history involved.

In another fold of the Great Yao Mountains, south-east from Wuxuan, the great Taiping Rebellion which rolled up half of China in 1951-64 began in the foothills of Mount Thistle. One of its leaders, the `western King' Xiao Chaogui, came from a Wuxuan peasant family and the Taipings' first military foray was launched into Wuxuan. Is this a clue to what happened a century later? Certainly the Taipings had a reputation for eating the hearts of their prisoners to make them bolder in combat (though so did the Manchu soldiers of the imperial armies with whom they fought). The official Party report also notes that, during the '40s, Japanese soldiers who raped Wuxuan women were sometimes killed and eaten.

These local factors help to explain Wuxuan's unhappy claim as the place where `we ate more people than anywhere else in China'. But why did it happen anywhere in a China which should have been transformed by socialism and the revolution?

For Zheng Yi, passionately anti-communist in the Solzhenitsyn mould, the answer is simple. The Communist Party and Mao were more savage, more inhuman, than Chiang Kai-shek or even Hitler and there is no need for further explanation. His sole concern is to reveal what has been covered up by timid or complicit party officials for the past twenty-five years. These and other dark secrets certainly do need to be exposed. It is impossible to imagine real political progress in China - whether towards pluralist democracy or a more democratic communist regime - unless Beijing can `settle accounts' with the past honestly and fully. The final reckoning will have to include the persecution of hundreds of thousands of intellectuals in the '50s (barely admitted because of Deng Xiaoping's role in this `anti-Rightist' campaign); the millions of famine deaths in the Great Leap Forward (only properly recorded in local histories which are not easily available); and the real responsibility for the Tiananmen Square Massacre which no one yet dares to admit. Cannibalism in Wuxuan is another such `negative lesson' to be learnt.

There is a broader justification, transcending China's own frontiers, for exploring these events. Crimes against humanity take many different forms, from Dachau to Dresden, from Angola to Cambodia, from the great Indonesian massacre of 1966 (when at least 100,000 died without the world noticing) to Wuxuan - and currently from Bosnia to Burundi. Why, we have to ask, does the impossible-to-believe somehow persist in happening? How can humans behave so frequently with such extreme inhumanity? The `special case' of Wuxuan is part of a much wider pattern which we need to understand.

In Wuxuan, as in most of China during the Cultural Revolution, a desperately poor community was expected to act out a political drama which it barely understood. Conflicting signals from Beijing destroyed the authority of those party officials who still believed in `serving the people'. If the people of Wuxuan had been as politically mature as Beijing propaganda pretended, and if they had enjoyed a reasonable standard of living and education, it might have been different. But control was seized by the ignorant, the insecure, the power-hungry and the pathologically violent. A primitive kind of class struggle did indeed take place in which those with more education and slightly better jobs (particularly teachers) were vulnerable targets. The rest was tyranny by a few, terror for the majority, and a growing mob hysteria.

Might it happen again in Wuxuan or elsewhere in Guangxi? It hardly seems possible as China moves into a new quasi-capitalist age. Yet the gap between the masses and the elite is still dangerously wide in the Chinese hinterland, and economic change is still far too slow. Only three hours by bus from the city of Liuzhou, where the streets glow with neon lights and the jewellery shops are always full, Wuxuan remains `backward'. Its young high-schoolers have only one ambition - to pass the national college exams and leave. Those who stay must settle into a society still isolated by physical and political barriers from hope and enlightenment. In this respect, Wuxuan is typical of a large swathe of China away from the booming coastal zones and rich provincial capitals.

Earlier this year I visited Mengshan County on the other side of the Great Yao Mountains. The Taiping rebels set up their first headquarters here in 1850 after they left Wuxuan. Mengshan, Zheng Yi tells us in Red Memorial, was notorious as a place where even the youngest children of `class enemies' were killed in 1968. Several were dragged to their death and dumped in an old air-raid shelter. One mother pleaded to be allowed to `keep just one' of her three children. Not one was spared.

Mengshan is now on a popular route for foreign backpackers, though their buses do not usually stop there. Surely there can be no child murderers now? I lunched in the town`s only good restaurant, next to a noisy table where bottles of Maotai liquor were being drained. The dozen men and one woman were hard-faced and swaggering, instantly recognisable as local bosses. I asked the waitress, already half-sure of the answer. Yes, this was `the leadership of Mengshan Public Security Bureau'.

Most of them would have been children themselves at the time when their peers were dragged to their deaths. Now they belong to a new exploiting elite which imports foreign cars, over-taxes the peasants and takes corruption for granted. Watching them belch and boast in the restaurant, lords of their domain, I could imagine them still getting away with murder. Or something even worse?