[UPDATE 11 PM: As mentioned in the post below, the layer for Rome is found under "Gallery->Ancient Rome 3D". However, this just loads the placemarks describing the key buildings. First, uncheck the "3D Buildings" layer. In order to see the Ancient Rome 3D models: 1) you have to click on one of the placemarks where you will see three links. 2) Click on the first link - which is the terrain for ancient rome (that hides the modern Rome and raises it above the new city. 3) Then load the second link which loads the 250 most detailed models. CAUTION: these models have a lot of complexity and you may need a newer machine with a fast graphics card to get these to load and update well. I'm sure Google will be working to simplify these models to make them load faster in future updates. If you load the third link with 5000 buildings - don't expect it to load all 5000 buildings at once. These buildings will only show when zoomed in close and only the nearby buildings will appear.]
For the first time, Google has published a 3D model of an ancient city as a layer viewable in Google Earth. For decades archaeologists, students, scholars, and architects have studied the history and remains of Rome and worked to understand the city’s history. The new layer, found under Gallery->Ancient Rome 3D, depicts Rome in the year 320 AD – at the peak of its development with over a million inhabitants. At this time it was the largest metropolis in the world. The 3D models are actually based on a physical model of the city called the “Plastico di Roma Antica” – created by archaeologists and model-makers from 1933 to 1974 and housed in a special gallery in the Museum of Roman Civilization in Rome. 3D digital models were created based on scans of the physical model. Google joined forces with the Rome Reborn Project and Past Perfect Productions to create the Ancient Rome 3D layer. Google helped convert the models into a format suitable for viewing in Google Earth. According to an interview with Bruce Poulderman of Google, there are about 200 buildings which are classified as “Class I” models which scholars and historians know a lot about and have been rendered as faithfully as possible.
The layer contains more than 6700 3D building models. You can learn more about some of the buildings by clicking on more than 250 placemarks on many of the key sites and the placemark descriptions link to more advanced information including a topographical encyclopedia, ancient literary sources and bibliographical information about each building. The layer’s placemarks are available in: English, German, Spanish, Brazilian Portuguese, French, Italian, Japanese, Russian, and Dutch.
See Google’s video introducing the layer:
An extra feature in the 3D city is that 11 buildings have viewable interiors – these include: Basilica of Maxentius, Colosseum, Forum of Julius Caesar, Ludus Magnus, Temple of Venus and Rome, Temple of Vesta, Regia, Basilica Iulia, Basilica Aemelia, Curia Iulia, Tabularium.
In order to avoid conflicts with the different modern day terrain and 3D models, Google chose to “float” the Ancient Rome 3D layer above the modern day city by a few dozen meters. You can speed up your performance a bit by turning off the 3D Buildings layer in Google Earth while using the Gallery->Ancient Rome 3D.
To help stimulate educational applications related to the Rome layer, Google has also announced “The Ancient Rome Curriculum Contest“. The competition is open to all K-12 educators (US Only) that will challenge teachers to produce lesson plans for their classrooms using the Ancient Rome 3D layer in Google Earth. Lessons for all subjects – from Art History to Engineering to Philosophy – are encouraged, and projects can be submitted in any format (KML, doc, ppt, skp), though KML and Google Doc submissions are encouraged. The deadline for submission is February 9, 2009. Six teachers will win prize packages including a laptop, classroom projector, digital camera, 3D mouse, $500 gift card, and a plaque. Read the web site for more details.
[UPDATE: See also Google's LatLong post, and Stefan has an informative write-up at OgleEarth.]