The mystery of an ancient Mesopotamian city has finally been lifted after 25 years of meticulous work by a French archaeologist who has revealed it was one of the first "modern cities", purpose-built in the desert for the manufacture of copper arms and tools.

In a new book entitled "Mari, the Metropolis of the Euphrates", Jean-Claude Margueron said the third millennium BC city, in modern day Syria, was "one of the first modern cities of humanity. Created from scratch in one phase of construction with the specific goal of becoming this metallurgical centre."

This was an astounding concept for the period when cities developed from villages or trading posts and showed that the Mesopotamians were way ahead of their time in terms of urban design and development.

"How could a city develop in the third millennium BC in the middle of the desert, in a region devoid of copper and in a valley devastated by the floods of the Euphrates making any agriculture very risky?"

In an interview with AFP, Margueron, 70, repeated the question which haunted him during the decades of excavations of Mari, discovered in 1933 by his predecessor Andre Parrot.

In 1935, the temple of Ishtar, the statue of King Lamgi Mari, then the Grand Palace of the second millennium, and other temples and fabulous sculptures were discovered, followed by the living areas and a part of the third millennium palace.

When Margueron took over as director of excavations in 1979, most of the spectacular pieces had already been discovered. But the question remained: Why had they built Mari?

To rediscover the city, Margueron spent thousands of hours examining the basements, the terraces, the living quarters, traces of streets, and the surrounding areas - the former river bed of the Euphrates and other waterways.

"So they were discoveries, not always spectacular, rarely immediately important, but very significant for the overall understanding of the site and its integration in the geographical, historical and economic context," said Margueron.

"The" revelation of Mari - spread over a dozen years but unpublished until now - was the existence of a major centre of metallurgy, dating from 2,900 BC.

"In fact the metallurgy was everywhere in the city. It was the existence of this lucrative activity - Mari produced arms and tools - which justified everything which we had found previously," said Margueron.

A major navigable canal was discovered which followed the Euphrates river for 120 kilometres (75 miles) and allowed the transport of copper and wood from the Tauras mountains of modern Turkey to support the metallurgical activities of Mari.

They also discovered an irrigation channel which allowed agricultural production in an area which otherwise did not receive sufficient rainfall to grow crops. A third canal protected the city from flooding and allowed large boats to enter the city which was also protected by a levy bank and double ramparts.

"The builders of Mari knew the profits they could make from a economic hub between the south of Mesopotamia and the north, between the east and the Mediterranean.

"The innumerable riches of the archaeological discoveries made during these excavations shows they were right."