OLDEST WOODEN STRUCTURE -- 6500 YEARS OLD -- FOUND IN THE THAMES, LONDON

The oldest wooden structure ever found on Thames river, timbers over 6,500 years old, have been discovered buried in the silt below the windows of British security services' headquarters at Vauxhall, south London.

The archaeologists who uncovered the six hefty timber piles had to explain to the security services what they were up to when armed police turned up after they were spotted pottering about in the mud, armed only with tripods, cameras and measuring equipment - not, as one spectator had apparently reported, shoulder-mounted rocket launchers. "They accepted there wasn't much damage we could do with a tripod," said Gustave Milne, the archaeologist who leads the Thames Discovery program that has been surveying the entire prehistoric foreshore.

The timbers, partly scoured bare by erosion of the river bed, the largest up to a third of a meter in diameter, were discovered in work during exceptionally low tides last February, but carbon dating work has only recently been completed, proving that the trees were felled between 4790 and 4490 BCE, during the Mesolithic period. Although the site is now exposed only at the lowest tides, the ancient Thames was narrower and deeper, and Milne believes that 7,000 years ago the timbers may have been built on dry land, possibly at the highest point of a small island. Structures of Mesolithic date are very rare anywhere in Britain.

"The find is very interesting, because in the mesolithic period the people were nomadic hunter-gatherers, living in temporary camps - not at all given to building substantial structures like this," Milne said. "At the moment we don't have enough timbers to give any kind of alignment, they're not in a straight or a circle - but they could have supported a substantial platform with some form of domestic structure or dwelling."

Kept secret until it could be fully recorded and investigated, the site is located at the confluence of the Rivers Effra and Thames. Near the timbers, late Mesolithic stone tools, including a fine tranchet adze (a woodworking tool), were also discovered, as well as slightly later Neolithic pottery of two distinct types. The area, may have been a significant, named place continuing through centuries or even millennia. It is only 600m downstream from the Bronze Age timber-built bridge or jetty (c1500 BCE) which hit the headlines in the 1990s. "There may have been a ford, it may have had some religious significance, or it may just have been very rich hunting grounds - but it was clearly what my colleague at the Museum of London calls 'a memorable place'," Milne said.

The site is affected by the scour created by the twice-daily tides and the growing river traffic. The remains are also threatened by planned riverside developments, including the much needed combined sewer overflow which will pass meters from the timbers. A major research project is under way.