I want a big city in the desert, what conditions make it possible?

Question

Starting condition: I know how small cities form. It is mostly a trade center that requires an access to water and food. But some cities have more than 100 000+ people.

• Climate: It is in the desert, an arid or semi arid climate, starting with the letter B according to this classification.
• Technology level: European middle age (late middle age to be more precise)
• Magic does not play an important role.

Result: A big city in the desert with several thousand people: 50 000-100 000 +

Process: How can I achieve a high population?

Answer 1

Basics of Life

Cities don't just happen. They exist where the basics of life are readily available. Whether or not the basics are there naturally is a matter for the history of your setting, but they must be there. You need...

• Water - I hope I do not have to explain why
• Food - Ditto
• Shelter - You need to be able to build homes; If there are no local building materials, you cannot have a city. You will have an outpost at best.
• Access - You need to be able to easily move in and out of the city. Cities in mountains rarely thrive without advanced transportation technology.

In the case of your desert city, you would need water (a river or springs, though it does not need to be enough to support the current city, just the first settlement), you need enough arable land to support that first settlement's need for food. You need access to wood or grasses to make structures. You need roads and/or rivers to travel on, which as you mentioned, would be the point of the city.

Need

The first settlement needs a purpose. Just being at a cross-roads is not enough - not every junction of the inter-state is a massive city. That location needs to serve a purpose. It must have a natural or artificial resource that a traveler would need. In my opinion, water is the most logical answer, however other needs are possible, including precious metal and mineral mines.

Technology

There needs to be enough engineering skill in the city to build infrastructure - irrigation, aqueducts, roads, sanitation, etc. These are more important in a desert than anywhere else. A small spring, which would be enough to support a small settlement would not support a large city as it grew - technology is how a city would solve that problem. Do not forget that cities themselves are systems of technology; the land would not naturally support that many people living in the same place. This would be an important point in your city.

Example: Las Vegas

The city of Las Vegas was formed as a small outpost on the road to the west (during the expansion of the United States to the west). It remained that way - an outpost for water and animal feed (and later gasoline) until the great depression, when water (from the brand new Lake Mead created by the hoover dam) became more abundant, with it came irrigation to grow crops and raise pigs. Shelter came in for form of artificial resources moved into the area by the government for the construction of the dam. With only these three, the city was a boom town in the classic sense - it served as a place for dam construction workers to waste their paychecks on vice. The city itself did not grow until the final basic of life was accomplished - access in the form of the national numbered roads system ('Highway system'). Without these four things, and technology to more efficiently use the four things, you cannot have a city, especially in a desert.

Answer 2

I would take a look at Baghdad. It is classified as BWh. It is on the Tigris river and as of 2011 it's population was over 7,000,000. For a city of any size in a desert, water is always the deciding factor. You need water to drink and to keep livestock and to grow food for one and all.

Oasis are another common way for smaller cities to grow up in the middle of a dessert, but to really get big you need a decent sized river.

Baghdad is on the Tigris and close to the Euphrates. Add to that it's in a good location for traveling caravans from the east it makes it a great market place where trade routes converge. For a town of any size to exist in such a location, you need of course a reason for a lot of people to go there. In the desert either it's a cross roads for trading or something (say easy gold) is there that people want. Often a trade routes will follow rivers or hop from one oasis to another.

Answer 3

Egypt would be another good example, the cities are based mostly around the Nile river and the river is responsible for the agriculture that takes place there. The Nile river would flood annually bringing large amounts of water for a few months but also silt with nutrients for crops down from mountains further south.

This was an important event in ancient Egypt; it was a holiday/festival and the astronomical signs were the basis for their calendar system (Details on these events)

Answer 4

In your question you stated the importance of trade in the formation of cities. It seems to me this is easily scalable. So long as there is sufficient water nearby (a river, as stated above), increasing the populations on either side of the city will increase trade, importance as a way station, and population. With sufficient trade, the desert's influence on food production doesn't matter anymore. This requires rather a higher level of civilization (but not technology) than the middle ages provided.

Also, if you don't want to put your city between two vast civilizations you could put down a mineral/ore deposit underneath (maybe the only [mythril] deposit in the world?) and attract trade and miners that way.