In this paper, I build on Ian Morris’ preceding article by exploring the preconditions for intensive economic growth in the Greco-Roman world. In section I, I reconsider the causes of intensive economic growth by placing Morris’ survey in a wider comparative context. Section II contains a very brief overview of demographic conditions in the ancient Mediterranean, followed by a discussion of the relationship between economic and demographic growth (section III) and the economic impact of ancient fertility regimes (section IV). I argue that institutional innovation and favorable environmental conditions had to converge to generate periods of concurrent demographic and intensive economic growth; that ongoing population growth eventually curbed advances in average living standards; and that the demographic structures of ancient societies were unlikely to constrain population increase even in the face of declining labor productivity.