In the Middle Ages, a cathedral took shape after decades of grueling labor by hundreds of craftsmen and laborers using hammers, chisels and wooden scaffolding.

The Cathedral of Our Lady of the Angels in downtown Los Angeles is going up in three years using the most advanced computer modeling and laser technology.

"This is a large, great city and we don't really have a great church," Mahony said last week during a site tour.

But that's changing quickly, as a forest of rebar rises skyward from the floor of the 5.5-acre site. Two cranes tower overhead while workers busily pour concrete in the early-morning hours. The cathedral walls are almost halfway to their ultimate height of 130 feet.

This is not your typical concrete building, either by church or construction standards. For starters, it is designed to last 300 years and withstand a major earthquake. By comparison, the typical office high-rise is designed to last 50 to 100 years.

Secrets beneath the walls

To add to the cathedral's longevity, 200 rubber pads called base isolators, imported from Great Britain, have been installed under the sanctuary and a separate campanile. The structures are encircled by moats covered with steel that can pop up, allowing a horizontal shift of up to two feet in any direction during a quake.

"Not one inch of the cathedral touches the ground," Mahony noted.

The cathedral's unusual shape, angled roof and curved walls also pose an architectural and engineering challenge. There are no right angles in the structure, and each of the 10 chapels lining the nave has a different shape, making the placement of all the building components much trickier than in a standard, symmetrical space. Lasers are used to direct that placement, based on coordinates supplied by a 3D AutoCAD program.

"It's very complicated, but that's also part of the beauty of the design," Mahony said. "You have to build a separate form for every single wall."

The roof will be supported by steel trusses at the top, above a cedar ceiling that will bow out slightly, like the bottom of a boat.

"That's where we've used computer modeling a lot, to make sure the roof trusses fit," said Nicholas Roberts, project manager with Leo A. Daly, executive architect for the cathedral.

Slanted shafts of light will flood the interior through windows of delicately veined Spanish alabaster. More alabaster will be used here than in any other church in the world. Mahony said stained glass was nixed because the windows are situated so high on the walls that visitors would have difficulty seeing the images, and because stained glass would make the sanctuary too dark.

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