A thought on reading Tamerlane

I have been reading Tamerlane: Sword of Islam, Conqueror of the World by Justin Marozzi. He happily describes populations of cities in Central Asia as being very large -- 150,000 for Samarkand in the time of Timur, for example. He also describes Timur's army as 200,000 strong, marching into Samarkand. Figures like that made me wonder about the factors that limit the size of a city's or an army's population.

Sanitation was a limiting factor in the past. Rome reached a population of a million people at its height, in part because it had an infrastructure of aqueducts and sewerage that could support so large a population. Lacking that kind of infrastructure, considerably smaller cities would stop growing because their death rates got so high that the balanced immigration (probably in part because people did not want to move to a city which appeared to be very unhealthy.)

Clearly it had to be possible to feed the city. I suppose one reason that cities often grew on the banks of navigable bodies of water was that water transport was an affordable way to bring food from afar, even before the advent of mechanical power and good roads or railroads.

The food going to a town or city had to be from the production of farms that exceeded the needs of the farmers. Subsistence farms don't support cities. In 14th century Central Asia, there was a history of irrigation, a fairly wide variety of crops, and a fair amount of animal power. The region also depended significantly on livestock that was herded by nomadic peoples, but who probably brought animals to urban markets in order to obtain other goods that they needed. The city was also apparently surrounded by orchards and vinyards, and the people managing the orchards and vinyards may produce more surplus per capita than other farmers. (i recall my days in Chile where you could buy very bad wine for nine cents a liter; it was the cheapest source of calories for the poor!)

Grazing lands could be quite distant from the city since cattle and sheep could walk to market. Similarly, there appeared to be a pretty good road system (at least for mounted messangers who provided a "pony express" linking Timur's widespread empire. One assumes that animal power was used to bring crops to market in the city.

A Tartar army supported its food needs by plundering the lands that it conquered, by hunting, probably by bringing livestock on the march for food, and probably by bringing supplies of grains by wagon or pack train. We are told that Timur's army could stay in the field for years at a time, and that it would camp around a town or city rather than seek to be quartered within the city. Still, one wonders wether 200,000 troops actually returned to Samarkand, or if they did whether they did more than march through town before returning to their tribal homes.

I have read that a number of ancient cities grew to the point where they so destroyed the local environment, for example cutting forests for firewood or overworking the land or water resources to the point that a drought or other environmental event could not be withstood.

It seems clear that these cities on the Silk Road also grew because the trade brought resources to the city which allowed it to acquire more of the food and environmental services that the population needed. The rare goods brought from afar were expensive enough that they would justify a fairly expensive trading infrastructure. Similarly, the plunder brought back from foreign conquests would pay for food and other services brought from afar for the small aristocratic class.

It might be interesting to do an economic model of the affordable size of cities. It would fit into the Zipf law relationships of the distribution of sizes of urban places.