The 14,300-tonne leaning Tower of Pisa moved north one-and-a-half millimetres last night, a sure sign that it is safe at last and unlikely to tumble over.
The good news was delivered at the British Association for the Advancement of Science's Festival of Science. Prof John Burland of Imperial College London is one of 14 experts who in 1990 were asked to rescue the tower, which has been threatening to fall for almost two centuries.
He suggested a technique to help stabilise the tower which was accepted after much debate and put into action early last year.
The idea was simplicity itself and came from his particular area of expertise, the science of soil structure and load-bearing.
The soil under the tower, he said, was a cross between jelly and foam rubber to a great depth, not the sort of neighbourhood suited to such a heavy structure. The most common rescue suggestion called for some form of support or underground foundation to hold up the low side of the tower.
Prof Burland took the opposite view, arguing that if soil were removed from the high side, the tower would gradually subside and slowly tip back towards the vertical.
The great problem was, however, that if one camp or the other got it wrong, the Leaning Tower of Pisa would quickly have become the Lying Tower of Pisa, an outcome the committee of experts hoped to avoid at all costs.
As Prof Burland noted however, "the one sure way to have it over was to do nothing".
Early in 1999 drilling teams moved in and began extracting soil from beneath the north side of the tower, which leans along a north-south axis.
Eventually the tower began to move, subsiding in a northward direction into the space left behind by the drilling. It had moved 1.5 millimetres last night he said, adding: "We are moving the tower at approximately five arc/seconds or 1.5 millimetres a day," and were steering it like a bicycle along its north-south axis.
So far the tower has been brought back 23 centimetres towards the vertical. The drilling team is about half way towards its goal of removing 30 cubic metres, 60 tonnes, of soil from beneath the edge of the tower and expects to finish by the end of 2000.
"We hope to bring it back to the start of 1838 when an engineer built a walkway around the tower that caused it to lurch," Prof Burland said. For all this movement, the public would probably not notice the change at all, he added. The relatively small shift would however allow the tower to be reopened to visitors next June 16th, 2001, since it was closed for safety reasons 10 years ago.