On June 10, 2000, Queen Elizabeth II opened the high-tech
Millennium Bridge, which traverses the River Thames from the
Tate Modern to St. Paul’s Cathedral. Thousands of people lined
up to walk across the new structure, which consisted of a narrow
aluminum footbridge surrounded by steel balustrades projecting
out at obtuse angles. Within minutes of the official opening,
the footway started to tilt and sway alarmingly, forcing some of
the pedestrians to cling to the side rails. Some reported
feeling seasick. The authorities shut the bridge, claiming that
too many people were using it. The next day, the bridge reopened
with strict limits on the number of pedestrians, but it began to
shake again. Two days after it had opened, with the source of
the wobble still a mystery, the bridge was closed for an
indefinite period. Some commentators suspected the bridge’s
foundations, others an unusual air pattern. The real problem was
that the designers of the bridge, who included the architect Sir
Norman Foster and the engi