David Galbraith studied the population of Rome over the last 3000 years. Interesting discoveries:

the rise and fall of Ancient Rome was roughly symmetrical (compared to the rapid decline of societies such as Greenland in Jared Diamond’s ‘Collapse’); the population during the Renaissance was miniscule (yet it was still a global center), when Michelangelo was painting the Sistine Chapel it was considerably smaller than a town like Palo Alto is today (60K); Rome at its nadir was about the size of Google (20K employees); the growth of Rome during the Industrial era is much greater than the rise of Ancient Rome.

Go look at the nice graph here.