The David Vases (made in 1351). Porcelain; from China

"In Xanadu did Kubla Khan

A stately pleasure-dome decree:

Where Alph, the sacred river, ran

Through caverns measureless to man

Down to a sunless sea."

The thrilling opening lines of Coleridge's opium-fuelled fantasy still send a tingle down the spine. As a teenager I was mesmerised by this vision of exotic and mysterious pleasures, but I'd no idea that Coleridge was in fact writing about a historical figure. Because Qubilai Khan is a thirteenth-century Chinese emperor and Xanadu merely the English form of Shangdu, his Imperial summer capital. Qubilai Khan was the grandson of Genghis Khan, ruler of the Mongols from 1206 and terror of the world. Wreaking havoc everywhere, Genghis Khan established the Mongol Empire - a superpower that ran from the Black Sea to the Sea of Japan and from Cambodia to the Arctic. Qubilai Khan, his grandson, extended the Empire and became Emperor of China, which leads us to the objects for this programme.

Under the Mongol emperors, China developed one of the most enduring and successful luxury products in the history of the world, a product fit for stately pleasure-domes, but which spread in a matter of centuries from grand palaces to simple parlours all over the world... it's Chinese blue-and-white porcelain. We now think of blue-and-white as quintessentially Chinese, but as we shall discover, this is not how it began. This archetypal Chinese aesthetic comes in fact from Iran.

"The fascinating thing about these vases is that they are so beautiful and mysterious, and yet they seem tremendously familiar." (Jenny Uglow)

"If you say Chinese porcelain, this is what you think of - this white background and this brilliant blue colour. But it hasn't been there for ever, it was a novelty at this period." (Craig Clunas)

The programmes this week look at high-status objects from all over the world around seven hundred years ago, objects which tell us about the taste and the ambitions - political and social, religious and intellectual - of the people who owned them. Thanks to the long Chinese habit of writing on objects, we know exactly who made the two blue-and-white porcelain vases in this programme, which gods they were offered to, and indeed the very day on which they were dedicated.

The importance of Chinese porcelain is hard to over-estimate. Admired and imitated for over a thousand years, it's influenced virtually every ceramic tradition in the world, and it's played a star role in cross-cultural exchanges. In Europe, blue-and-white porcelain is practically synonymous with China. And we've always associated it with the Ming Dynasty. But it was the David Vases, now in the British Museum, that made us re-think this history, for they predate the Ming and were in fact made under Qubilai Khan's Mongol Dynasty, known as the Yuan, who controlled all of China until the middle of the fourteenth century.

Seven hundred years ago most of Asia and a large part of Europe were reeling from the invasions of the Mongols. We all know Genghis Khan as the ultimate destroyer and the sack of Baghdad by his son still lives in Iraqi folk memory. Genghis's grandson Qubilai was also a great warrior, but under him Mongol rule became more settled and more ordered. As Emperor of China, he supported scholarship and the arts, and he encouraged the manufacture of luxury goods. Once the Empire was established, a 'Pax Mongolica' ensued, a Mongolian peace which, like the Pax Romana, ensured a long period of stability and prosperity. The Mongol Empire spread along the ancient Silk Road and made it safe. It was thanks to this Pax Mongolica that Marco Polo was able to travel from Italy to China, and then return to tell Europe what he'd seen. And one of the startling things he'd seen was porcelain.

The David Vases are so-called because they were bought by Sir Percival David, whose collection of over one and a half thousand Chinese ceramics is now in a special gallery at the British Museum. We've put the vases right at the entrance to the gallery, to make it quite clear that they're the stars of the show. David acquired them from two separate private collections, and was able to reunite them in 1935. They're big, they're just over two feet (60 cm) high and they're about eight inches (20 cm) across at the widest, with an elegant shape, narrowing at the top and the bottom, swelling into a full central body. Apparently floating between the white porcelain body and a clear glaze at the top, lies the blue, made of cobalt and painted in elaborate patterns and figures with great assurance. There are leaves and flowers at the foot and at the neck of the vases, but the main body of each vase has a slender Chinese dragon flying around it - elongated, scaled and bearded, with piercing claws and surrounded by trailing clouds. At the neck are two handles in the shape of elephant heads. These two vases are obviously luxury porcelain production, made by artist-craftsmen delighting in their material.

Porcelain is a special ceramic fired at very high temperature: 1200-1400 degrees centigrade. The heat vitrifies the clay, so that like glass it can hold liquid, in contrast to porous earthenware. And the heat also makes it very tough. White, hard and translucent, porcelain was admired and desired everywhere, well before the creation of blue-and-white.

The very word 'porcelain' comes to us from Marco Polo's description of his travels in Qubilai Khan's China. The Italian 'porcellana', 'little piglet', is a slang word for cowrie shells. They do indeed look a little like curled-up piglets. And the only thing that Marco Polo could think of, to give his readers an idea of the shell-like sheen of the hard, fine ceramics that he saw in China, was a cowrie shell, a 'porcellana'. And so 'little piglets', porcelain, we've called it ever since - that's if we're not just calling it china. I don't think there's another country in the world whose name has simply become interchangeable with its defining export.

The savagery of the Mongol invasion destabilised and destroyed local pottery industries across the Middle East, especially in Iran. So when peace returned, these became major markets for Chinese exports. And in these new markets blue-and-white ware had long been popular. So the porcelain the Chinese made for them mirrored the local style, and Chinese potters used the Iranian blue pigment, cobalt, to meet local taste. The cobalt from Iran was known in China as 'huihui qing' - 'Muslim blue' - clear evidence that the blue-and-white tradition is Middle Eastern and not Chinese. Here's Craig Clunas, an expert on Chinese cultural history:

"Iran, and what's now Iraq, are the kind of areas where this sort of colouring comes in. This is a technique that comes from elsewhere, and therefore it tells us something about this period, when China is unprecedentedly open to the rest of Asia as part of this huge empire of the Mongols, which stretches all the way from the Pacific almost to the Mediterranean. Certainly the openness to the rest of Asia is what brings about things like blue-and-white, and it probably had an impact on forms of literature. So from the point of view of cultural forms coming into being, the Yuan period is extraordinarily important."

And among the happy consequences of this cultural openness are the David Vases. The crucial significance of the vases is that as well as their decoration, they have inscriptions - inscriptions that tell us that they were dedicated in the year 1351, in fact on Tuesday 13 May 1351. It's a level of precision that's wonderfully Chinese, and it's proof positive that fine quality blue-and-white porcelain pre-dates the Ming. But the inscriptions tell us much more than that. There are slight differences between the inscriptions on the two vases, but this is the translation of the one on the left:

"Zhang Wenjin, from Jingtang community, Dejiao village, Shuncheng township, Yushan county, Xinzhou circuit, a disciple of the Holy Gods, is pleased to offer a set comprising one incense-burner and a pair of flower vases to General Hu Jingyi at the Original Palace in Xingyuan, as a prayer for the protection and blessing of the whole family and for the peace of his sons and daughters. Carefully offered on an auspicious day in the Fourth Month, Eleventh year of the Zhizheng reign."

There's a lot of information here. We're told that the vases were purpose-made to be offered as donations at a temple, and that the name of their donor is Zhang Wenjin, who describes himself with great solemnity as a disciple of the holy gods. It gives his home town, Shuncheng in what is now Jiangxi province, a few hundred miles south-west of Shanghai. He was offering these two grand vases along with an incense-burner - the three would have formed a typical set for an altar. The incense-burner has been lost, or at least has not yet been found. The specific deity receiving the offering had only recently become a god. He is General Hu Jingyi, a military figure of the thirteenth century, who was elevated to divine status because of his supernatural power and wisdom, and his ability to foretell the future. Zhang Wenjin's altar set is offered in exchange for this new god's protection.

Foreign rulers, the Mongols; foreign materials, Muslim blue; and foreign markets, Iran and Iraq; all played an essential part in the creation of what to many outside China is still the most Chinese of objects, blue-and-white porcelain. Soon these ceramics were being exported from China in very large quantities, to Japan and south-east Asia, across the Indian Ocean to Africa and the Middle East. And far beyond that. Here's author Jenny Uglow:

"Then it comes to Europe, and the Dutch adapt it to their life, and so it comes to Britain, and we adapt it to the forms of jugs we like, the plates we love, and so on. It becomes translated, it's like a wonderful language which is perpetually translated to the culture where it's arriving and is loved. People say it's a very, sort of, elemental thing: it's blue and white, it's the blue sky and the white clouds, or the blue sea and the white sand. And behavioral psychologists who've looked at the way people react to colour say that blue and white is seen as immensely serene and relaxing. But I think also it has to do with the great long history - you know, a thousand years of history - and the way that the blue-and-white designs themselves seem to be mysterious and 'other' and have their own stories as well. It's a combination of colour appeal and historical appeal."

So, eventually, centuries after its creation in Muslim Iran, and its transformation in Mongol China, blue-and-white arrived in Europe and triumphed. Willow-pattern, the style that many people think of when blue-and-white is mentioned, was invented in England in the 1790s by Thomas Minton, and it was as much a fantasy view of China as Coleridge's poem. It was an instant success, and Coleridge may indeed even have been drinking his tea out of a willow-pattern cup as he emerged from his opium dream.

Blue-and-white porcelain was the first truly global luxury product, and one that could be infinitely adapted to suit all local tastes. The David Vases, the earliest dateable blue-and-white, were made as offerings to the gods; in the next programme we're with another high-status object, also used as a means of connecting with the supernatural... it's a ritual throne from the Caribbean.