An age-old custom, the Yaji, or Festival of Summer Pleasures, is one of many occurring simultaneously across Kham, a former Tibetan kingdom of towering mountain ranges and rolling grasslands in the far reaches of eastern Tibet. Large or small, flashy or plain, every village organises some sort of show in late May or early June. The carnivals are leftovers from the great clan gatherings, when the nomadic warrior tribes would meet to settle disagreements about land, leadership and who had the fastest horse. Forever locked in endless bloody feuds, sometimes handed down through generations, the festivals were designed as week-long armistices, taking, in theory, disputes off the battlefield and into the sporting arena.

Ponies, tassels suspended from forelocks, tails plaited with ribbon, saddlecloths embroidered with flaming dragons and saddles embossed with the Buddhist Wheel of Life, gallop along racetracks, while their riders shoot at paper targets with their antiquated rifles and snatch silk scarves from the ground. Others jump and twirl as they bring tribal dances to life - the men macho, the women delicate and poised, their sleeves flowing and their ankles ringed with bells.

THE SERXU FESTIVAL IS THE biggest and most authentic in Kham; last year's event attracted more than 10,000 nomads and villagers. A small town 4,200 metres above sea level and hidden in the heart of eastern Tibet's desert grasslands, Serxu typifies an outpost: dusty, remote and peopled by a procession of nomads stocking up on supplies. The journey to Serxu, requiring three days' driving on a treacherous road from the nearest airport at Chengdu, is not for the faint-hearted. Those with no alternative walk for weeks across mountain ranges and windswept plains to attend. They line the showground with their white festival tents and decorate themselves with their finest furs, silks and jewels, indulging in a riotous round of socialising, drinking, dancing and singing.

Culturally Tibetan, the Khampas are warriors: formerly they were nomadic bandits who put the fear of God into the heart of every traveller who passed their way. Called 'gentlemen brigands' by early 20th-century French explorer Alexandra David-Neel, the unruly but devout Buddhists typically have vigilant, almond eyes, faces flushed by sunlight, high cheekbones and long, lightly splayed noses. They are strikingly handsome cavaliers.

They swagger in fox-skin cloaks, one arm free, the other sleeve hanging down to their knees, their heads wrapped in bundles of red silk, necks festooned with turquoise, amber, coral and ivory. Riding ponies valued also for their strength and stamina, they roam the grasslands, tending their yaks and training their steeds for the festival. On the grasslands of Tibet, where roads are at a premium, owning a horse is imperative. To own a fast and agile beast is to be honoured, envied, feared and respected.

Horse festivals were banned during the Cultural Revolution of 1966-76, when almost every Kham monastery, temple and shrine was looted and razed. The festivals officially re-emerged in the 1980s, but Kham's more accessible celebrations have had their authenticity sacrificed for the sake of political approval, and present growing numbers of mainland and foreign tourists with an officially sanctioned version of events.

Yushu, in the mountains of Qinghai to the east of Tibet, is home to one of the oldest horse carnivals. An ancient trading hub through which tea and salt passed from China to Tibet, Yushu has become a sprawling grey metropolis retaining few of its traditional rammed earth and log houses, offering in their place skyscrapers and brothels.

Its festival now has a strong Chinese flavour and features displays of military might and expressions of allegiance to the motherland. In a specially built stadium soldiers parade with AK47s; Khampa boys carry larger-than-life posters of Mao Zedong and Chinese national flags while loudspeakers scream, 'Make China stronger!' For some Khampas, this festival looks more like a party fair than a warriors' convention.

It is the third time Tsering has made the journey from London to Yushu. Born in a tent on a windswept plateau in Amdo, another traditional Tibetan kingdom, Tsering walked to India at 12 and now holds an Indian passport.

'The festival is changing,' he says. 'Each year it becomes a little less Khampa and a little more Han Chinese, with a few more tourists to pay for the frills.' Complete with cowboy hat, knee-length leather boots and silver belt buckle depicting a yak's head, Tsering looks like a true horseman, albeit one of mixed East-West pedigree. He sheepishly admits, however, that his costume is saved for horse-racing festivals.

As at most equestrian events, fashion is critical, but here it can also have lasting implications: long, treacherous winters make travel impossible for much of the year, meaning summer is an occasion for more than mere socialising. For many horsemen it is also time to find a wife.

Elegant and impeccably turned out, Khampa women lead the way in festive finery. Their robes, called chubas, are embroidered with brocade; their hair is waxed, plaited into an auspicious 108 braids and studded with turquoise and coral before being pinned under a traditional summer sun hat, which is topped with more brocade. Buddha boxes containing pictures of celebrated lamas hang from slim waists, cheeks are reddened with the best make-up affordable and feet are tucked into traditional felt boots with upturned toes. This is the model of grassland beauty.

IF THE FESTIVALS WERE once crucial to the survival of a nomadic lifestyle, today they are essential to the survival of Khampa culture. China's occupation of parts of Kham in the 1950s ultimately led to the dissolution of its borders with Han China, the kingdom being seized for the creation of a buffer state between China and Tibet that would act as a springboard for Chinese attacks on capital Lhasa.

The Khampas, fighting with little more than swords and fists, held their ground initially, but the Chinese hit back with heavy artillery and air raids and stationed 300,000 troops throughout the kingdom. The Khampas were driven further into their hinterland as the Chinese military pressed on to Lhasa, capturing the city in 1959.

With CIA encouragement, Khampa guerillas regrouped in the old Himalayan kingdom of Mustang, now in Nepal, in the early 1970s, but were abandoned to the Nepalese army, who killed all those who refused to disarm, when the United States shifted its attention to Vietnam.

'A lot of Khampas have given up resisting the Chinese now,' says Tsering. 'They realise it is easier to cooperate. They can take our land, our amulets and our pictures. The Government can tell us what to do, what to wear and how to act, but they can't take away how we feel in our hearts. The Chinese are in control and the nomads are disappearing. Even the monks at the festival are false,' he declares. Rumours have it that while many monks struggle to keep their monasteries open and independent, a nearby gompa receives funds from the Government, which dictates what can be taught. Beijing keeps it 'well stocked and clean, and the monks happy with silk robes and new motorbikes', claims Tsering.

His parents, he says, still roam the grasslands of Amdo, yaks in tow, preferring a life in a tent to what Tsering describes as life in a 'germ-infested hovel of a Chinese town'. Many of Kham's remaining nomads, however, do not have the luxury of that choice. Grasslands are becoming privatised, sold to farmers who fence them off and prohibit grazing. The Government also has other plans for the ancient kingdoms of eastern Tibet, including gas extraction, the resettlement of city dwellers and the construction of a railway line, which may presage agriculture and mining.

Perhaps as a result, and thanks to a relaxation of regulations, Kham has witnessed revivals in faith and culture, with many monasteries destroyed during the Cultural Revolution being rebuilt under the direction of lamas previously in exile. Their advances have been small so far, but the Khampas retain a beguiling culture and implacable sense of identity and spirit.