Introduction

1Few past civilisations have had such a central notion of government as the Roman Empire, with the possible exception of the Han Empire in China (Scheidel 2009 ; 2015). One person, the Roman emperor, at the helm of a single city, Rome, was meant to rule the world. The city of Rome made up ca. 1.8 % of the estimated total population of 50-55 million within the whole Roman Empire, while approximately 13.2 %, or ca. 6.6- 7.26 million, lived in other urban areas. In AD 300, the city of Rome counted one million people. It was the largest city in the world. In AD 550 the population had dwindled to a mere 30-50,000 people (Durliat 1998 ; Scheidel 2007). No longer a coherent urban unit, Rome had fragmented into separate villages and fortified compounds on seven different hills with fenced-off vegetable gardens and grazing livestock in the valleys. No other city in the world would reach the 4^th century population figure of Rome until some 1,300 years later, when Beijing, Ch