Archeologists have found few images of early imperial Rome. A fire-often, but probably mistakenly, attributed to Nero-razed much of the city in A.D. 64. Many of the grand monuments of empire-the Colosseum, the Pantheon-were built over the next few centuries. This fresco, which some archeologists believe was painted shortly after the fire, may be a depiction of that old city. Archeologists discovered it last March in an underground passage beneath the Baths of Trajan, near the Colosseum. The exposed portion of the painting measures about 12 feet long by 9 feet high. More of the fresco may be buried beneath rubble on the floor. The mural is a bird's-eye view of a metropolitan city, showing houses, temples, enormous public monuments, and a large central hall, all surrounded by a stone wall topped with tall towers. Toward the back of the painting a bridge spans a wide river that may be the Tiber. The topography of the painted city, however, does not match Rome's, so it may be an idealized version of the city, or another city entirely, perhaps Alexandria or Carthage. Ongoing excavations may settle the issue of its identity.