Today, a clever Roman engineer outsmarts himself. 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.
Historian Henry Petroski writes
about failure. After all, success has far less to teach
us than failure does. He goes to Vitruvius's
1900-year-old book on Roman engineering. Vitruvius tells
about a proud engineer named Paconius. Paconius bid on
the job of moving the pedestal for a statue of Apollo.
The pedestal was a stone block, 12 feet by 8 feet by 6
feet -- about 50 tons of stone.
The Romans knew a lot about moving stone. To move a
cylindrical column they'd drill axles into the ends, then
tow it like a big roller. For a square column, they'd fit
wooden wheels around the ends, then build a frame around
the wheels and tow it like a cart.
But Paconius's pedestal was an unusual job and he had his
own scheme for handling it. He built a great
15-foot-diameter horizontal wooden spool around it. Then
he wrapped the spool with rope. The end of the rope came
over the top of the spool and was attached to several
yokes of oxen. As the oxen pulled the rope, the spool was
to roll forward, playing out the rope.
It seemed to make sense. But try rolling a spool of
thread forward by pulling on the thread. As long as the
thread's wound in the middle of the spool, it works. But
when the thread's off to one side, the spool slews away
from the direction you're pulling. I'll read what
Vitruvius says about Paconius's attempt:
As [the rope] uncoiled, it did indeed cause the
wheels to turn, but it could not draw them in a line
straight along the road. Hence it was necessary to draw
the machine back again. Thus by this drawing to and fro,
Paconius got into such financial embarrassment that he
So Paconius went bankrupt and Petroski looks for a moral
in his story. Paconius did what any inventor must: he
began by looking for an idea within his own head and he
came up with a good one. But good designers also have to
know how to attack their own idea. They invite others to
attack it. They look for anything that could be wrong
with it. Vitruvius says,
"Paconius, with confident pride ... determined to make a machine of a [new] sort." The
key word there is pride. It takes a dimension of humility
to question our own ideas. Proud Paconius wasn't able to
So he missed what a good critic might've seen. Petroski
goes on to tell about modern designers who've brought far
greater disaster on themselves in the same way.
But Paconius's story also harbors a second, and more
subtle, message. Rome was conservative and so was
Vitruvius. Rome capitalized on older inventions but added
few of her own. Vitruvius portrays Paconius as foolish
for wanting to "make a machine of a [new] sort." That
lack of vision eventually caught up with Rome. She needed
more Paconiuses -- more makers of ideas.
Good engineering is the flight of imagination within the
constraints of reality. Engineering can't flourish
without Paconius any more than it can flourish with
people like Paconius alone.
I'm John Lienhard, at the University of Houston, where
we're interested in the way inventive minds work.