Its creator has called it a "virtual time machine" – a digital reconstruction of ancient Rome that today became available to hundreds of millions of internet users around the world.
Users of Google Earth can now see the city, down to the last aqueduct and arena, just as it looked at midday on April 1 AD320. They can float through the Forum, past the platform or "rostra" from which Cicero once declaimed, admire the statues, read the inscriptions, pry into palaces, and then slip round to the Colosseum or whisk over to the Circus Maximus where the ancient Romans held their chariot races.
There, the virtual traveller will find, not the slightly disappointing, though enormous, oval expanse of grass that confronts the real tourist, but the huge, walled stadium that tourists are forced to conjure up from their imagination.
It is the "Rome of [the emperor] Constantine in which everything is new", said Google Earth's chief technologist, Michael T Jones, at the presentation in Rome's city hall. "It's new. It's modern. It's beautiful".
All that the awe-inspiringly detailed reconstruction lacks is people. Their absence gives a slightly eerie feel to the stadiums and temples, the marketplaces and thoroughfares of classical Rome.
Some 6,700 digitally reconstructed structures have gone towards making up Google Earth's latest layer, which can be superimposed on its images of the city. Users can enter ten of the buildings, including monuments such the Colosseum, where the software enables them to marvel at the architecture and even gaze on details like marble floors whose exact shape and pattern are known because their remains have survived to the present.
The first concerted effort to "recreate" the ancient imperial capital was made by an Italian architect, Italo Gismondi. Three years before his death in 1974, he finished a vast, plaster model of ancient Rome in 1:250 scale that can be seen in the city's Museo della Civilta Romana.
Gismondi's research played an important role in the digital project, which was begun in 1997 by a teacher at the University of Virginia, Bernard Frischer. After 10 years of work and collaboration between his own university, UCLA in California and Milan's Politecnico, Rome Reborn – made up of 50m polygons (the building blocks of three-dimensional computer graphics) – was unveiled last year.
The job of transferring it to the web was shared between Google's 3D unit and a Rome-based firm, Past Perfect Productions, run by a Briton, Joel Myers. He said today it had taken 15 people the best part of a year to complete the operation.
Myers said Rome Reborn was "the largest and most complete reconstruction of an ancient city". Its creator had chosen 320 AD "because it was Rome at its moment of greatest splendour as far as its architecture is concerned. If you went back to periods of more historical interest, like Julius Caesar's, you would not have the Colosseum, for example."
Rome's mayor, Gianni Alemanno, said he hoped the project would get over a "problem of communication" that the city had noted with its visitors who increasingly demanded something more than just ruins. "Obviously, providing a monumental, archaeological reality is fundamental", he said. "But for many people it's insufficient, it's too remote."
And, in a sense, it is much smaller too. Of the real classical Rome, just 300 buildings – and, in most cases, their remains -- have survived.
