It is very problematic trying to estimate the number of slaves in Rome , even as a percentage of the population. Due to a relative scarcity of specific mentions in primary historical sources most estimates are based on modern scholarship (eg. the debate between [Scheidel] (http://www.princeton.edu/~pswpc/pdfs/scheidel/091003.pdf) and the likes of Jongman) using comparative approaches, such as slave numbers in antebellum American South (See the quite extensive, Marshall (ed.) 'The Archaeology of Slavery: A Comparative Approach to Captivity and Coercion'). Slaves in the ancient world are relatively 'invisible' archaeologically. Some things that we can look for are shackles at villa sites etc., though these are extremely rare (with metal often being melted down rather than simply abandoned) and even contentious. Or we can look to suspected slave quarters, like at the [Settefinestre Villa] (http://en.wikipedia.org/wiki/Settefinestre) in Italy, and attempt to estimate how many slaves could have been housed here (although the identification of the slave quarters at Settefinestre is based largely on the size of the rooms anyway, and is again a contentious issue). So even for specific sites, estimating numbers of slaves can be difficult, and although estimates for the percentage of the population that were slaves in Rome have been made (possibly 15-25% in imperial Italy according to estimates discussed in Scheidel), the emphasis, even, to an extent, for total population never mind slaves specifically, is definitely on estimate, with limited scholarly consensus. I am sure that an expert specifically concerned with Roman slavery could offer a more specific answer, but it is important to be aware of the difficulties associated with our understanding (or relative lack thereof) of slavery at Rome.

Classics honours specialization here.

Are you referring to the full territorial holdings of Rome at the time, or the city of Rome?

Either way it's difficult to guess. Spartacus led his revolt, the Third Servile War, just a few decades after the date you mentioned.

Appian mentions that Spartacus had around 120,000 followers, but to the best of my knowledge most of his slaves were recruited from southern Italy, with few if any coming from the city of Rome itself. Of course, Appian had no way of knowing truly how many men Spartacus had.

He lived nearly 200 years later, and the slaves didn't exactly take a census of how many people they recruited.

On top of that, no accounts from the slaves themselves survive. Those who were captured in the final battle with Crassus were crucified. A few thousand escaped, only to be captured and slain by Pompey's forces.

Nevertheless, Appian's number is the best we have to work with as far as I know.

Spartacus' group focused their activities in the south of Italy, mainly on the east coast. It's probably safe to say they weren't able to liberate every slave in these regions.

According to Bruce W. Frier's "Demography", the Roman Empire had a population of about 45 million in 14 AD, and about 15% of those were slaves.

7 million of them lived in Italy. Since it was the centre of the empire at the time, it's conceivable that there may have been more slaves living there than in the rest of the empire.

Anyway, that's all I've got. Hope it sheds some light on your question!