A great city is not to be confused with a populous one.
Urizen is a hilly and mountainous land that appears inhospitable at first glance. The Urizen dwell in secure settlements they call spires, built on plateaus, the summits of hills or mountainsides. The difficulty of producing food means that the population of most spires is relatively small. Most spires keep large herds of goats that provide meat and milk and feed on the thin grass that grows on the hillsides below. This is supplemented by fruit and vegetables specially cultivated in arboretums and gardens. Most spires use magic to ensure that harvests are sufficient to feed everyone who depends on them, but there is rarely much in the way of surplus.
Spires tend to be large and airy; stone is plentiful and the Urizen prefer open plan chambers, designed to let light flood into them. Chambers are usually joined by short paths, but it is not unknown for individual Urizen to dwell an hours walk or more from the main body of the spire. A typical Urizen is used to having plenty of space to move around in, and plenty of privacy to get on with the things that interest them. Spires are often heavily fortified, but this is usually achieved by creating a central keep and building defensive walls and gates to protect the narrow paths needed to reach the summit, rather than attempting to wall off the entire community. To the Urizen life is rare and precious but space is plentiful so it makes sense to protect the former and not the latter.
When the population of a spire begins to grow too large to feed itself, they will begin construction on a new spire – usually on a nearby hill or mountain peak. When the new spire is largely complete, a proportion of the original population moves to the new spire. The two spires maintain a relationship a little like that of a parent and child until the “child” spire is “mature” enough to be self-sustaining, at which point a formal ceremony is held in which the two spires become independent groups. Political ties often remain close between the two spires.
Sometimes a new spire is formed because a group within an existing spire disagrees with the way things are run, and occasionally just because a group wants to try something new. These spires are less planned, and more prone to failure.
Often two (or even three or four) spires will co-operate to create a new spire, mingling their populations in doing so. The newly created spire may be built to help each spire deal with their growing population but it may also be created as a means to exploit a specific resource, or as part of a political agreement between the participants. Regardless of the reason for forming the spire, the assumption is that eventually it will become independent of the parents once it is self-sufficient.
The idea of one group directly controlling more than one spire in Urizen is generally considered laughable. A combination of the problems caused by the mountainous terrain, coupled with the resentment that grows within a few generations of someone else telling them what to do, is seen as leading inevitably to bloody revolt, which is the last thing any Urizen wants to see.