The growth of urban civilization conceals a major paradox. Clearly, the formation of the city-states of the Middle East and ancient Greece is good evidence for increasing population. The urbanization of Western Europe was also accompanied by an overall increase in population. What is rarely appreciated is that, until relatively late in the industrial era, the death rate in the cities was higher than the birth rate. Consequently, the populations of medieval cities were replenished by migration from the countryside. During most major periods of city growth, the population increases were actually produced in rural areas; the cities themselves had a net negative impact on the population.