Tourists puzzled by the jumble of buildings in classical and modern Rome can now find their bearings by visiting a virtual model of the imperial capital in what is being billed as the world's biggest computer simulation of an ancient city.

"Rome Reborn" was unveiled on Monday in a first release showing the city at its peak in 320 AD, under the Emperor Constantine when it had grown to a million inhabitants.

Brainchild of the University of Virginia's Bernard Frischer, Rome Reborn (www.romereborn.virginia.edu) will eventually show its evolution from Bronze Age hut settlements to the Sack of Rome in the 5th century AD and the devastating Gothic Wars.