In 1974 a group of Chinese peasants sinking a well on scrubby land outside the city of Xi’an discovered some fragments of terracotta. As the work progressed, one side of the well disappeared into an underground pit. If they had started digging a few feet in the other direction, they would have missed the subterranean chamber altogether. One of the wonders of the world might then have remained undiscovered and the British Museum would not now be preparing for what is expected to be its biggest exhibition.

Ancient sources referred to the tomb of the First Emperor of China, and the huge burial mound was visible above ground. But there was no mention of what the Emperor had buried with him: an entire army of terracotta warriors to guard him in the afterlife. The roof of the pit had collapsed, shattering the figures into pieces that had to be painstakingly reassembled. “At first we were not sure what they were,” says Yuan Zhongyi, the first director of the site. “It was a year before we realised the significance. We found inscriptions on the weapons that linked them to the first Emperor. It was very exciting to find so many objects. There had never been a find like this before. It was not only me that was surprised. People from all over the world were excited.” Other pits were discovered containing not just warriors but other terracotta members of the imperial court. The sheer scale of the mausoleum slowly became apparent. It now is known to cover more than 50 square kilometres. The four main pits yielded the majority of the finds, but there are some 600 pits in total, some containing artefacts, some seemingly the remains of ceremonial buildings. So far about 1,900 figures have been recovered. It is estimated that there are as many as 8,000 figures in total in the pits that have been located.

Qin Shihuangdi united the warring kingdoms of China and became emperor in 221BC. He not only unified the country, but also formalised the language, the code of law, the coinage and the system of weights and measures. He brought together a number of walls on the northern frontier to create a barrier that was a forerunner of the Great Wall of China. He established an empire that was to last until the beginning of the 20th century, and the Western word “China” is thought to be derived from his name (Qin is pronounced “Chin”.)

He was a megalomaniac who became obsessed with finding an elixir that would give him eternal life. The next best thing was to be all-powerful in the afterlife, and he was apparently convinced that the way to do this was to surround himself with perfect, baked clay models of the soldiers, officials, servants and entertainers that he would need.

Today, walking to the head of pit number 1, looking down at the massed ranks of restored warriors as they stare past you in the direction from which enemies would approach the Emperor’s tomb, one is overwhelmed by the astonishing creative feat of mass-producing this army. The sheer number of warriors is awe-inspiring and leaves the observer wondering how this stunning visual impact can be transferred to an exhibition in London.

After elaborate negotiations the Chinese authorities have agreed to allow 120 pieces to travel to Britain. These will include 20 terracotta figures, of which 12 are warriors, as well as a bureaucrat, a musician, an acrobat, a strongman and a chariot and horses. Among the other objects will be bronze birds, intended to amuse the Emperor during musical performances in the nether world. This is the largest collection yet to have been allowed out of China.

Neil MacGregor, the director of the British Museum, says that he is delighted by how many objects have been secured and predicts that it will be “the biggest and most important exhibition we have put on, certainly the biggest in terms of scale. The only comparison would be Tutankhamen”. This is a reference to the 1970s show that became “the first blockbuster exhibition”, but The First Emperor is already setting new records – 36,000 advance tickets have already been sold.

“You can’t replicate the experience of seeing the mass of figures,” says MacGregor. “What I want to do is really give the visitor the experience you can’t get here.” The emphasis will be on allowing visitors to get very close to the figures in a special space being created in the Reading Room.

In Xi’an MacGregor and his entourage are given the rare privilege of being allowed to walk in among the figures in the main pit. This serves to prove his point about the value of seeing the warriors close up: it is a different, but similarly humbling, experience.

It is believed that the figures are not portraits of the real inhabitants of the Emperor’s world. Rather, they were mass-produced using moulds and then exquisitely individualised by each craftsman with a variety of facial features and tweaks of hair and attire. What makes their creation all the more intriguing is the fact that there was no tradition of figure making before the emperor embarked on this hubristic enterprise.

Standing among the larger than lifesize warriors, MacGregor speculates about the process of their creation. “The care taken with each one is miraculous. The people who made them must have really enjoyed doing it,” he says. Someone suggests that they were created by forced labour and joy must have been absent. “But there is so much more detail here than it needs,” argues MacGregor, staring at the delicate definition on a face. “It’s hard to imagine you wouldn’t enjoy doing it.”

The higher ranks got paunches and bigger bottoms, possibly a sign that fun was being had by the serfs at their masters’ expense. Or is that a 21st-century interpretation? Perhaps this was just an indication of their well-fed prosperity. More than 2,000 years later it is hard to say.

The tomb mound itself, which ancient texts reported ran with rivers of mercury, has barely been touched because of sensitivities about disturbing the sleep of the First Emperor. Technology may eventually allow a delicate exploration of the site, but it may never be opened. In any case, archaeologists have years of work to do on the huge mausoleum complex. “I hope there won’t be any more discoveries because of all the conservation work required,” says Wu Yongqi, the current director of the site. “But the ordinary people hope that we carry on finding things.”

MacGregor, whose eyes light up at the prospect of more buried treasure, takes the contrary view: “I’m with the ordinary people.”

The First Emperor: China’s Terracotta Army, The British Museum, Great Russell Street, London WC1 (www.thebritish museum.ac.uk 020-732 38181), from Sept 13, £12, concs £10. A fully illustrated book is also available from The British Museum Press, priced £40

OFFICERS, NOT GENTLE MEN – LIFE IN QIN’S TERRACOTTA ARMY

The expressive faces of the soldiers in Qin’s Terracotta Army and the delicately sculpted details of each rank make it tempting to assume that the statues were modelled on real individuals. Experts say not. Yet faced with this silent throng, one can’t help but wonder what their lives were like.

It appears that the Qin Dynasty did not maintain a professional army but ensured that all ranks were ready and able to perform duties as and when the state required. Adult males would have completed military service as part of their tax obligations. They were registered once they had reached a height of 4ft 11in, at around the age of 16, until they retired, between the ages of 56 and 60, irrespective of rank.

On the field, a set of strict written laws governed how officers could punish their men, largely peasants who are believed to have marched into battle to the sound of drums and bells and the waving of flags and banners.

A general’s power was symbolised by the ceremonial giving of the axe. It was presented by the ruler to the commanding general in a formal ritual as a symbol of his legal authority to kill the enemy and execute any officer or man who dared to disobey his orders.

Experts believe that until a general had returned the axe even the ruler could not countermand his orders in the field. A general’s rank was further marked by his armour. He wore a helmet with a hole in the side for his hair knot, which he wore low, unlike his men who wore their hair knotted on top. His armour extended down as far as his waist, with a triangular extension covering the abdomen made of some 250 scales held together by coloured ribbons, straps and buttons.

The extra protection would have come in handy as battle groups swelled and campaigns grew longer under the First Emperor, Qin. Soldiers would have suffered gruesome injuries from weapons such as swords, dagger-axes, halberds, spears and crossbows. Little wonder armies already had doctors – and vets – in tow. NICKY CHATTERTON

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