The Muqaddimah: An Introduction to History

Cities only arise with dynasties, since their construction requires organization by political authority and the excess wealth produced by a stable, sedentary state. They also serve the dynasty as a peaceful oasis and a strong point of defense (especially with walls and clean air to prevent disease). Only fools believe that giants must have built great urban monuments of the past; regular people did, albeit sometimes over the course of several dynasties.

The size of towns fluctuates with the fortunes of the dynasty but ultimately depends on the amount produced from trade, crafts, and agriculture. Spending on buildings and crafts in a city always becomes equal to overall income and affects even the poor. Although food may be cheap, other costs are higher in developed cities as people take advantage of surpluses to compete for luxuries and workers to produce them. This keeps poorer Bedouin out of the city.

Larger countries can effectively utilize vast pools of labor to produce surpluses and that makes their people comparatively richer than people with smaller or no civilization. They create a tradition of sedentary culture that can survive dynasties if widespread, although a new dynasty will often destroy a particular city, such as the previous royal capital.