I just finished Robert Harris’s Imperium which is very good. I was wondering how much of the Rome of Caesar is still part of modern Rome. I have searched for a virtual Rome but have not had much success. The funny thing is, I was in Rome many years ago but do not remember much (I was young!). I know the Coliseum is there but what about the ancient walls? Was it ever abandoned as a city?
If I could add to my own question, it appears that the Colosseum (various spellings) was not built until well after Caesar. What did they use for their sporting spectacles before then?
A lot is still there, but the city has grown organically over more than two millenia, so there is a lot of attendant layering. For example, the Piazza del Campidoglio (Capitoline Hill plaza) is built on top of ancient buildings. The Palazzo Senatorio is built on top of the Tabularium (a sort of record hall; you can see a picture of both buildings on Wiki . I think the columns in the foreground are what remains of the Temple of Saturn, which doubled as a treasury); the Palazzo dei Conservatori is built on the Temple to Jupiter. The medieval church Santa Maria in Aracoeli is built near where the Arx (Temple to Juno) was located. It doesn’t take a rocket scientist to realize the sort of ideological connections being made with such a placement.
The Republican Forum is in shambles today as much of the marble was cannibalized in the Middle Ages and Renaissance for other projects (sadly, often the marble was burned down into lime for concrete). This can be said for a lot of the ancient monuments, not least the Colosseum (at one time the Colosseum was also used as a church). There were also bronze bindings that held the blocks together; often they were dug out of the marble and melted down, resulting in a lot of the damage you see today.
Rome Reborn 1.0 has some nice virtual video clips of what some parts of the ancient city could have looked like.
As for whether it was abandoned, well it came pretty close a few times. Roma was but a shadow of her former glory after the sacking in AD410 by Alaric the Goth. But it was inhabited continuously since at least the 8th century (legend attributes the founding of the city by Romulus to 753BC, and archaeological evidence backs up this time frame). The Republican Romans had an ancient hut that was maintained to be the home of Romulus himself. It was often damaged in fires, course of time, etc. and usually reformed exactly as before. “Where it was, as it was” was a ruling doctrine WRT to the maintenance of buildings. This sort of attitude is still prevalent today; La Fenice, an opera house in Venice, has been burnt down and rebuilt twice. The second time it burned down (1996), it was rebuilt exactly as it was and exactly where it was in its previous incarnation.
The area that the Republican Forum is located in was used for burial going back to the 13th century BC. There were some things going on in the Forum that not even Augustan age Romans really understood (I’m thinking specifically here of the Lapis Niger).
For some interesting reading, I recommend Mirabilia Urbis Romae, this being a 12th century guide for pilgrims to the city. You can pick the MUR up for way cheap and it’s fun reading.
On preview: the Colosseum was completed under Titus in AD80. It was so named after the Colossus of Nero, which the megalomaniacal emperor had installed as a portrait of himself. The head of the statue was later replaced with a representation of the sun god. Formerly, spectacle games would have been held in temporary arenas.
And now that I have wracked my brain and spent 20 minutes writing all that, I am sure someone will be along shortly to nitpick it to death. 
Here is an interesting–if frustrating link.
It displays a map of “ancient” Rome (without specifying a year) with various buildings highlighted (but not named). Rolling the cursor across any of those images pops up a photo of the building in its current condition. (I believe the image is looking Nortwest with the Vatican to the right of the picture (across the river) and the Capitoline obscured by the text box in the upper left.
The Pantheon is also intact and probably the best preserved of all ancient Roman buildings.
I like to think the HBO series “Rome” gives an accurate picture of the Roman social and cultural upperclass mores of 100 BC. If that is true, then those morals and culture are firmly alive in todays upper class Mafia circles, as depicted in that other HBO-series, Soprano’s.
Yes, I know they’re both dramatized fiction. Still, it’s fun to ponder the psychology.
the Rome of the TV series is not what we think of as Rome in its glory days. That came later - it was the Emperor Augustus’s boast that he had “found Rome built of brick and left her built of marble”.
The Mausoleum of Hadrian, now the Castel Sant’Angelo, is one of the most prominent remains of Rome’s glory days
I have just one thing to add to Queen Bruin’s excellent post.
Historians are typically fond of saying that there was no single day or event that truly marks the fall of the Roman Empire. When the last emperor’s reign ended, either in 476 or 480 depending on who you consider to be the emperor (Romulus Augustulus or Julius Nepos), life went on in tne near term just as it had done before. But there was a single disastrous event that reduced Rome to a shadow of its former self – the cutting of the acqueducts by one of the barbarian invaders of the 6th century. I think it was Witigis, but I’m not sure and I don’t know the date. After that there was no running water. Imagine for a moment how that would be in your city if it happened right now.
Queen Bruin - no nitpicking here. No time to try, anyway 
But yes, as she said, before the Colosseum was built, Romans usually erected temporary structures made of wood for their games, shows and plays. The first major permanent structure was the Theatre of Pompey, and it was used as well.
The Circus Maximus was the Republic playground for centuries before the fall of the Republic.
That’s the famous model of Rome by Italo Gismondi in the Museo della Civiltà Romana at EUR. It shows Rome during the reign of Constantine. The model has been widely reproduced, including as the establishing shot of Rome in Gladiator.
As Queen Bruin has mentioned, the earlier games were held in temporary structures. Those were usually erected in the Forum. Some of the details are discussed half way down this page.
We visited Rome a year ago for the first time and I was surprised how much of the ancient city was visible through the overlying layers - however robbed out, demolished etc. As well as the major ruins - the Colloseum, the Palatine, the various Forums (Fora?), etc, and the almost intact buildings adapted for other uses, the Pantheon, the Castel Sant’ Angelo (Hadrian’s Mausoleum) etc, - there are lots of smaller sites that you find at random as you walk through the city.
There are not much of the really ancient Servian walls visible but the 4th century AD Aurielian wall are still there and still very impressive.
And underground, both parts of the Catacombs and of the ancient drains can be visited.
And some of the pizza slices in the tourist kiosks have been there since at least the time of Augustus 
Everyone else seems to have ignored this bit, so I’ll answer - no, the city has been continuously inhabited more or less since its founding, although there have been any number of minor evacuations/exodoi due to fire, pestilence, et cetera.