LOS ANGELES, CALIFORNIA.- By reconstructing the Roman Colosseum with three-dimensional computer modeling and then virtually "walking through" it, researchers have discovered that in some sections the building may have been very inefficient. The model reveals dark, narrow upper hallways that probably hemmed in spectators, slowing their movement to a crawl. Such three-dimensional modeling is turning some of archaeology’s once-established truths on their heads. Because 3-D software can take into account the building materials and the laws of physics, it enables scholars to address construction techniques in ways sometimes overlooked when they are working with two-dimensional drawings. "Now we have a tool that will really test assumptions," said Dean Abernathy, a doctoral student who helped reconstruct the Colosseum at the Cultural Virtual Reality Lab at the University of California at Los Angeles. "It creates a lot of excitement in the field." The U.C.L.A. lab (www.cvrlab.org) creates models of architectural sites around the world. Since 1996 it has been working on a project called Rome Reborn, which seeks to rebuild much of the ancient metropolis.

The Colosseum, a vast four-story oval arena, was built from around A.D. 70 to 80 under the rule of the Emperor Vespasian and then Titus. It once held as many as 50,000 spectators. Earthquakes and the ravages of time have destroyed much of the building, but an impressive amount, including most of its facade, still stands. Mr. Abernathy confronted the issue of the third-level hallways when he was working on the reconstruction. His model drew on the findings of a team of experts on Roman architecture assembled by U.C.L.A. who had studied similar amphitheaters, drawings of the Colosseum and records of the building’s construction and expansion. The team also examined what was left of the upper hallways, an area that had previously been all but closed to researchers.