Today, we visit the Leaning Tower of Pisa. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
outreached themselves. The Gothic buildings that
stand are a remarkable legacy. But we don't see the
failures. Well, that isn't entirely so. We see a
few. In fact one failure, the Leaning Tower of
Pisa, is a marvel to see.
The Leaning Tower, like many other old Tuscan
towers, sits on soft soil. It's only one of many
that've gone askew in various ways. But none is
more dramatic. Its height, after 800 years of
tilting and sinking into the soil, is about 184
I always thought of the Tower as a Renaissance
building, but it's older than that. Its
construction began way back in 1173. When builders
finished the first third, they found it'd tipped
0.2 degrees to the northwest. So they put it on
hold for a century. By then the tilt had extended
to 0.7 degrees.
Yet the city fathers resumed construction anyway.
Masons squared off the top of the tilted stump and
built upward. The Tower tilted again, this time to
the north. They stopped again. For another century
the Tower sank and tilted — to the north, to the
east, and finally to the south.
With the Tower now leaning almost 2 degrees to the
south, work went ahead once more in 1373. Masons
squared off the top a second time and finished the
Tower. Now the top was straight, but the lower
portion had a gentle but permanent corkscrew shape.
The Tower has continued tilting at an average rate
of 21 seconds each year. Now it moves only 7
seconds per year, but that's cold comfort when it
leans almost 5½ degrees off vertical —
nearly a 10% tilt.
And so it stands, majestic and eerie -- defying the
rules of fall that Galileo was supposed to have
learned on its summit. Walk with me to the top. The
stair coils about the outside. You cringe against
the wall each time you negotiate the south face and
hang over empty space. You reach the summit, short
of wind, and gaze out over the ancient intellectual
center of Pisa. But there's one more tight circular
staircase. Take a deep breath and mount it. Now you
gaze down, even on the bells. Nothing more
separates you from the blue Tuscan sky.
And all the time you wonder what medieval magic
keeps the Tower from abruptly finishing its fall
while you stand there. Civil engineers have learned
what its medieval builders did not know about
foundations, but they haven't learned to end the
Tower's movement. With an animal obstinacy, it
curbs experiments. It responds to each measure by
tilting faster. It teases our minds with its crazy,
slow-motion, corkscrew fall.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds