an average of figures from different sources as listed at the US Census Bureau's Historical Estimates of World Population; see also * Kremer, Michael. 1993. „Population Growth and Technological Change: One Million B.C. to 1990“, The Quarterly Journal of Economics 108(3): 681 – 716.
The range of figures from different sources as listed at the US Census Bureau's Historical Estimates of World Population put the population at 1 AD between 170 million to 400 million.