Mother of all pearls: A very precious gem

Kublai Khan liked to show his admiration for the young Venetian trader Marco Polo in many ways. Enthralled by the stories that his witty young European guest told as the pair reclined amid the splendour of the Mongol emperor's stately pleasure dome at Shang-tu - better known as Xanadu - he rewarded him with one of the most powerful positions in the Eastern world. He made him governor of the wealthy trading city of Hangzhou and a trusted emissary.

Polo repaid his host's faith by performing his often-hazardous diplomatic missions with sensitivity and success.

In fact, the young Italian found himself a little too indispensable to what was to prove the last of the great Khans and the mighty conqueror turned down his repeated requests to be allowed to return to Venice.

Eventually, after 17 years in his service, Polo was allowed to go home. As he set off on his last mission for the Khan, escorting Princess Koekecin to her marriage to the Ilkhan Arghum, he had in his possession another token of the Mongol ruler's esteem. It was a giant pearl, around the size of a chicken's egg. But what made the 575-carat gem, weighing some 115 grams, so special was not just its outlandish size and obvious huge monetary value but its extraordinary beauty. Pink, blue even brown hues shone out from its creamy surface.

Kublai Khan gave the pearl - now known as the Arco-Valley Pearl from the Austrian dynasty which owned it for much of the last century- to his departing guest.

Insured for $5m (£2.5m), it was expected to raise almost twice that in an auction last night, butthe Abu Dhabi company handling the sale postponed the auction just hours before the biddding was expected to start becuase of a death in the Emirates Royal Family.

Lifestyle Auctions said the son of the Emirates' education and science minister, Sheik Nahyan bin Mubarak al Nahyan, had died in a car crash yesterday. No new date for the auction was announced.

If sold at its high estimate of £4million, carat for carat, the pearl would be twice as expensive as all but the most sought after diamonds.

According to the auctioneer Paul Fletcher, pre-sale interest has been intense and he has refused repeated requests to reveal the identity, nationality or any other details about the seller for fear of creating a "paper trail" that could be traced. For as well as attracting deep curiosity among the booming oil kingdom's battalions of super-rich, it has prompted something of a rivalry with Abu Dhabi's extraordinarily well-off neighbours in Dubai.

But, says Mr Fletcher, there has also been an unexpected surge of inquiries from representatives of China's growing ranks of billionaires. They would like nothing better than to return the pearl to what they say is its original home, he says.

"We had an astonishing response from China when we first announced the sale," recalls Mr Fletcher. "They insisted it was a national treasure and should come back so here is their opportunity to make it happen."

Despite its extraordinary provenance, the Arco is nowhere near the largest pearl ever discovered. That accolade is accorded to the Pearl of Allah - a monster nearly three times its size, discovered by a fisherman off the Philippines island of Palawan in 1934 and stored in a local museum. It has never been offered for sale. What fascinates collectors is the extraordinary story and beguiling mysteries surrounding the Arco.

Research carried out in Dubai suggests that the stone almost certainly predates the birth of Kublai Khan in 1213, possibly by as much as 200 years.

Pearls were a symbol of high rank in Egypt from as far back as the 5th century BC. The Greeks believed they were formed when lightning struck the sea while the Romans thought them to be the frozen tears of the gods.

In China they were first recorded even further back, although the oldest known item of pearl jewellery was found in the sarcophagus of a Persian princess who died in 520BC and which is displayed in the modern day Louvre.

Such was the desire among the Chinese, they began culturing pearls from the fifth century - an artificial process in a which a bead is inserted into a oyster to stimulate the creation of the sought-after nacre or mother of pearl.

But the Arco-Valley Pearl is no man-made object. It was probably formed in a protected Pacific lagoon after a tiny particle of organic material entered the shell of the mollusc.

Until the 20th century pearls were harvested by divers after diligently sifting tons of oysters to find gem-yielding shell.

According to Mr Fletcher, the first known owner of the pearl was Genghis Khan, grandfather of Kublai. The fearsome warrior, whose empire stretched from Kuwait to Korea and Russia to China, ceded control of his conquests and his wealth to his grandsons. Analysis of drill marks on the gem reveals that jewellers from before the 12th century worked on it with tools long superseded by the time of the reign of the Khans.

One theory has it that it formed the centrepiece of a ceremonial mandarin suit. Later it was drilled to be attached to a crown or turban decorated with precious stones belonging to a Persian king. In more recent centuries it was part of a European noblewoman's tiara. But, according to Mr Fletcher, most experts now agree that the first European to see it was Marco Polo.

The Polos had established their business in the Venetian quarter of Constantinople, but ever fearful of attack, they relocated to Soldia in the Crimea - narrowly escaping the sacking of their former home and the blinding of its Venetian citizens. Marco Polo's father and uncle pressed ever eastwards, eventually meeting Kublai Khan in present-day Beijing. He sent them home, armed with a message for Pope Clement IV requesting Western teachers to be sent to help his people. The Polos returned three years later, this time accompanied by the young Marco.

"From what we know Kublai Khan and Marco had a wonderful personal relationship," says Mr Fletcher. "He loved the stories he told about the camaraderie of his travels and his bravery,"

When Polo returned to Venice in 1295 few believed his stories about his life in the distant palace of the great Mongol king. In his book Il Milione - known to English readers as The Travels of Marco Polo - he recalls being forced to show doubting friends evidence of his claims by revealing the many precious stones lavished upon him by the Khan.

After his death in 1324 the trail of the pearl goes cold.

By the 14th century, the wearing of pearls was strictly controlled with many ranks and professions banned from wearing them. Soldiers believed they would keep them safe in battle.

At some point Polo's gem passed into the possession of the Arco-Valleys - with whose name it has now become synonymous.

Perhaps the most notorious figure to bear the family name was the aristocrat Anton Graf von Arco-Valley. His assassination of the Bavarian socialist leader Kurt Eisner in February 1919 - an event which despite his Jewish ancestry (his grandmother was a member of the Oppenheim banking family) - was celebrated by the Nazis. Arco-Valley escaped the death sentence thanks to a lenient judge. He went on to serve five years at Landsberg prison, eventually vacating his cell for a young Adolf Hitler.

The organisers of the sale hope that the auction will mark a new phase in the pearl's long and colourful history. They also believe it will help restore to Abu Dhabi, what they believe to be its rightful position as the capital of the world's pearl trade, a position it occupied until the 1930s when the discovery of oil in the waters of the Gulf spelt disaster for the industry. Pearl divers had been harvesting the seabed for 7,000 years until the search for black gold proved a more lucrative and easier option.

The proceeds from the auction will be used partly to fund a travelling pearl museum to promote the industry, with the rest going to a children's charity.