I noticed that there are four smaller semicircles cut out of the sides that are equidistant between the larger ones. They each have what looks like five roads radiating out from them. What could those be? Maybe former Department of Immigration (or whatever equivalent there is) offices that got closed down after the Wall started being built, and now they've been taken over by homeless people?

...Actually, looking at the startlingly symmetrical layout of the city, maybe the whole place is a rune, used to power some titanic spell?

Hey [@Mokley], how's that for a plot? =P