What is a city? Since everyone knows what a city is the question seems unnecessary, but the answer is not as simple as it might seem at first sight. A city, for example, is not just a very large town. As we saw in the last chapter, population is sometimes suggested as a marker, ranking anywhere with more than a hundred thousand inhabitants as a city. But London's largest borough, Harrow, has a population of more than a million, and it is certainly not a city. Furthermore, there have been quite small cities – Periclean Athens and fifteenth century Florence spring to mind – which have been amongst the greatest cities in human history. What is it, then, which defines a city? Joel Garreau lists industry, governance, commerce, safety, culture, companionship, and religion as the function of cities, and on those grounds argues that Edge Cities are proper cities. All these too, however, could be found in large boroughs which were not properly cities. Jane Jacobs wants to define the city in terms of consistent generation of economic growth from the local economy. In her view any settlement that becomes good at import-replacing becomes a city.