The control room of the Leaning Tower of Pisa is not very impressive, as control rooms go— just a handful of technicians and computers in a construction— site trailer. But if the tower ever decides to stop leaning and start falling, those technicians will be the first to know. Every five minutes the computers receive data from 120 sensors inside the tower that monitor its inclinations. The tower has its harmless daily moods. In the late morning it leans away from the sun, like some giant antimatter sunflower, tilting imperceptibly northwest as its southeastern side warms up and expands. At night the tower settles back to its current southward tilt of around 5.3 degrees.
It is that persistent angle that is alarming. It is bigger than it sounds or than it looks on postcards. When you walk the streets of Pisa, and the tower pops into view for the first time, it is shocking— the visual equivalent of a prolonged screech of brakes. For a split second you wait for the crash. People have been waiting for centuries, of course, and so you might reassure yourself that the crash can't really happen. After all, it is hard to imagine 177 feet and 32 million pounds of marble simply falling, in an instant, after 800 years. But some people have no trouble imagining it. "It is pretty terrifying," says John Burland, a specialist in soil mechanics at Imperial College in London. "The tower is literally on the point of falling over. It is very, very close."
Not quite as close as it was last year, though: Lately the tower has been moving ever so slightly in the right direction. From his London office Burland is supervising a delicate operation in which dirt is being extracted through thin drill pipes— the geotechnical equivalent of laboratory pipettes— from under the north, upstream side of the tower foundations, allowing it to settle toward the upright direction. The rate of soil extraction amounts to just a few dozen shovelfuls a day; anything faster might jolt the tower over the brink. Its condition is considered so precarious that it has been closed to visitors for a decade: The top leans a full 15 feet out of plumb. Burland and his colleagues on an expert committee appointed by the Italian government are hoping to bring it back 20 inches by next summer.
There are 13 members of the committee, but Burland, for this crucial operation, is the "responsible officer." Every day he gets faxes from the control room in Pisa telling him how the tower is doing; every day he sends back instructions on where to remove dirt next. He takes care to sign his messages. "That's absolutely essential," he says. "Someone's got to take responsibility. Unless you do that, you get another Black September." Burland is referring to September 1995, when it seemed for a while as if the committee, which was charged with saving the tower, might manage to knock it down instead.
In 1902 the campanile collapsed in St. Mark's Square in Venice, and the Italian government appointed an expert committee, the third, to consider what to do about the Leaning Tower of Pisa. In 1989 another medieval bell tower collapsed in Pavia, south of Milan, killing four people, and the Italian government appointed its 16th (or 17th, depending on who's counting) expert committee to consider what to do about the leaning bell tower of Pisa. Burland had never been to Pisa and little knew how his life was about to change when he took a phone call early in 1990 from his friend Michele Jamiolkowski, a geotechnical engineer at the Polytechnic in Turin. Burland remembers the conversation this way:
