Well, here's something that might come in handy...

Google Earth now has a 3d rendering of Rome 340AD. It lets you stand in the Forum, walk throught the arena of the Colosseum, the Arch of Constantine, explore 6700 buildings and the detailed interiors of 11 structures including the Temple of Venus, the Temple of Vesta, and the Basilica of Maxentius.

Each building has been carefully reconstructed and positioned using historical records, recreating the biggest and most important metropolis of the ancient world.

Of course, if you are writing about ancient Rome, be prepared for smart-arses to start emailing you now, telling you Mark Antony should have turned left not right at the end of the Appian Way in his triumph through Rome.

(To which, of course, you can respond, Mark Antony wasn't in Rome in 340AD...tee hee)

Google Earth Ancient Rome