The 1,200-year-old sunken treasure that revealed an undiscovered China

The journey began in a noisy, provincial factory that churns out concrete pillars for the German building industry. It ended with cities bidding for the world's largest collection of ninth-century Chinese treasure

The journey began in a noisy, provincial factory that churns out concrete pillars for the German building industry. It ended with cities bidding for the world's largest collection of ninth-century Chinese treasure

Tilman Walterfang, 47, was works director at the concrete company, miles from the sea in Germany. Now he presides over a multimillion-dollar haul of Chinese treasure discovered in the seas of south-east Asia.

Mr Walterfang's fascination with submerged wrecks began when an Indonesian employee described the translucent, reef-strewn waters of his native island of Belitung, between Borneo and Sumatra. Treasure, he said, lay under the waves.

The stories were irresistible. Mr Walterfang packed his scuba gear and flew to Indonesia with his employee. The trip was intended to be only a summer holiday diving adventure but it changed Mr Walterfang's life.

He chucked in his job and moved to Indonesia. Swapping central Germany's grim industrial landscape for white, palm-fringed beaches and the azure blue Java sea, he lived in a waterfront villa that belonged to an former Indonesian government minister.

Mr Walterfang read intensively about the rich maritime history of the region, for centuries among the world's major ocean thoroughfares, which is still infested with pirates. He made friends with fishermen, divers so poor they use improvised breathing-masks fed with air pumped from the surface through garden hoses, instead of gas bottles, to reach the ocean's depths. Above all, Mr Walterfang dived too.

He followed a lead provided by his fishermen friends who had presented him with a handful of broken pottery they had gathered during a dive. Donning his black, neoprene wet-suit and diving bottle he plunged 50ft down to a reef off Belitung.

"I landed on what looked like an ordinary section of coral reef," Mr Walterfang told Germany's Der Spiegel magazine. "But it was actually an underwater mound the size of a small hill that was built almost entirely of tens of thousands of pieces of well-preserved ceramic pottery."

That was six years ago. His discovery was the second of three wrecks - the third being the Tang - which has turned out to be an undersea treasure trove of such massive historical significance that Shanghai, Singapore and Doha in Qatar are vying with each other to buy the cargo. The 60,000 pieces Mr Walterfang collected from the seabed, include porcelain ceramic wine jugs, and tea bowls, embossed golden and silver chalices and plates found to be 1,200 years old.

The treasure was part of a huge cargo of eighth-century porcelain that traders from the Chinese Tang dynasty had put aboard an Arab dhow for export to Malaysia, India and what is now Saudi Arabia. The dhow's remains, found among the treasure, suggest the ship was wrecked on the treacherous underwater reefs of Indonesia's Karimata straits on its outward voyage through the Java sea.

Until Mr Walterfang's find, archeologists had assumed that 1,200 years ago, China was a relatively backward country which relied primarily on agriculture to survive. They had little notion that the Tang dynasty of the period, had already started to set up maritime trading routes that were to establish China as the first great sea power, 200 years before the Spanish, Portuguese and British had theirs.

Yet the "Batu Hitam wreck", as Mr Walterfang's find is described, has forced them to alter their perception of ninth-century China radically. John Guy, curator of the Indian and South-east Asian section of the Victoria & Albert Museum said: "Sometimes things happen which dramatically broaden the limits of our knowledge. The discovery of the Tang period wreck is such an event."

Archeologists say the Batu Hitam wreck provides incontrovertible evidence that, 1,200 years ago, China had started sea trade as an alternative to the then well-established Silk Road that extended from China through Asia to the Arab world. The overland route was fraught with problems: in the eighth century the Chinese had not yet developed the skills to bake pottery to present levels of durability, so many of their exports arrived at their destinations shattered and broken.

Export by sea became the logical alternative. Yet, as the Batu Hitam wreck has established, the Chinese were at first forced to rely on the expertise of Arab seamen who had perfected the dhow as an ocean-going vessel, to export their goods. But the wealth China created through its maritime exports enabled the country to build its own navy. By 1237, China was the predominant global sea power, with 52,000 seamen manning a vast fleet.

Tilman Walterfang's collection including blue, and green and white porcelain pieces, 22 silver and seven gold chalices and plates is now stacked in a closely-monitored aircraft hangar in New Zealand. The banks of shelves containing the priceless objects are 15ft high.

The first clues to the age of the treasure were provided by inscription on the bottom of two glazed bowls recovered from the wreck which dated them as being from the "16th day of the seventh month of the second year of the reign of Emperor Yingsong", which established 826 as the date.

A second clue came from the remains of an aniseed and raisin concoction that had been hermetically sealed from the ravages of time and water in an earthenware jug. Radio carbon analysis in New Zealand showed that the contents dated from between 680 and 890.

A third clue was an inscription under the heavily corroded metal of a bronze mirror which established the item had been smelted "100 times" in the city of Yangzhou on the Yangtze river in December, 758.

Evidence that the cargo played a key part in China's eighth-century global export drive was provided by a chemical analysis of the wreck, which showed that the 90ft vessel was built of Indian and African wood as an Arab dhow.

Michael Flecker, the Australian archeologist who worked on the wreck said: "We can assume the ship was manned by Arabs and Indians who had intended to sail back from Yangzhou to one of the caliphates of the Arab world when they were wrecked in a storm off Belitung."

Final proof that the treasure was authentic was provided by 81-year-old Professor Doc Geng Baochang, the deputy director of Peking's Forbidden city and China's foremost expert on antique ceramics. He believes the treasure belongs to China.

Yet Shanghai is the only Chinese city bidding for the collection. Archaeologists hope the eventual buyer of the treasure, which is now in the final stages of desalination, will showcase the collection in its own museum to display the unique time capsule from China's golden age.