There's a project called Rome Reborn where researchers have created a 3D model of Ancient Rome circa 320 AD. Check it out, and particularly the videos at the bottom of this page!

http://romereborn.frischerconsulting.com/gallery-current.php

There are two notable scale models of Ancient Rome. The older one is located at the University of Caen, in France. It is 1:400 scale and was finished in 1900.
http://www.unicaen.fr/cireve/rome/pdr_maquette.php?fichier=historie&langue=en
The other, even more impressive model is located in a museum in Rome itself. Commissioned by Mussolini in 1933, this 1:250 scale model was not finished until 1971.
http://www.ssqq.com/travel/barcelona2009romereborn.htm