In Libya, again open to U.S. travelers after more than two decades, archaeologists have uncovered spectacular mosaics of the glories of RomeHelmut Siegert returned to the coast of Libya last year to follow up on a tantalizing discovery. In September 2000, his colleague Marliese Wendowski was excavating what she thought was a large farmhouse when, 12 feet deep in the sandy soil, she came across a floor covered with a stunning glass-and-stone mosaic of an exhausted gladiator staring at a slain opponent. The discovery had come too late in that year's expedition to pursue further, so the University of Hamburg...