Today, an inventive mind plays with building blocks. 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.

In San Antonio the other day, a friend said, "John, I want you to see something." He took me to the backlot of the Zachry construction company. We looked at a long row of concrete forms -- each the size of a large room. Nearby was a casting from one of those forms. It was a 33-foot cell block -- four solitary confinement cells, all cast in a single piece of concrete.

The company was building a prison from these pieces -- stacking them like Leggos. This strange outdoor assembly line produces large buildings, one room one at a time.

Later that night, my wife and I strolled on the River Walk. We passed under the Hilton Hotel, looming 21 stories straight up. It was made from a stack of Zachry's concrete rooms. So we walked into the elegant lobby where the desk clerk said, "Sure, take a look." She lent me a key to a room on the 20th floor.

The room was lovely, but hard to believe. All this luxury had been cast in the same mold as that four-man cell block. I touched a picture on the wall. It was bolted solidly in place. It had to be. They'd completely finished and furnished each thirty-five ton room before a crane carried it into the sky. They could let nothing rattle around loose.

I leaned out over the balcony to see where the room was joined into place. Everything fit within a quarter inch. Think how hard it is to place a 35-ton room as it swings on the end of a cable, twenty stories up. To do that, Zachry engineers invented a strange gadget. They attach a vertical propeller to each room as it rides the crane. The propeller came straight from the tail of a helicopter, complete with its control system. It holds the rooms rock-steady as they fly into position.

The economics of these buildings is a surprise. They don't cost any less. Still, they give an owner a terrific financial edge. This hotel went up in less than seven months. It went into service long before a hotel whose concrete was poured high above the street. It drew income far sooner. It was the speed of its construction that increased profits for its owners.

I have here a statement of the builder's "Philosophy" -- his one-page credo. Such things are always overblown. People shouldn't try to express the inexpressible before they've honed a poet's skill. Yet one line comes through with odd clarity. "I want to dream and to build," he says. "I want to fail and to succeed." I believe him. For if his cravings had been any less grand, he would never have created such a radical technology.

I'm John Lienhard at the University of Houston, where we're interested in the way inventive minds work.

The Hilton Palacio del Rio Hotel and the H.B. Zachry Company in San Antonio both provide useful promotional materials that tell more of the story I've told here. The hotel rooms were built in just two sizes: 32-2/3'x9.5'x13' and 29-2/3'x9.5'x13'. This hotel has 496 such rooms. A certain amount of conventional concrete work has been used for the larger rooms -- especially on the lower floors. But time is really saved by finishing the bee- hive of individual rooms on the ground. The quality control in the concrete work is better, as well.