These cities are actually colossal retrofitted terraforming syringes. (It is basically a .5 mile diameter, 6 mile long syringe that used gravity to violently inject thousands of tons of needed elements toward the planet core.) The IEF dropped 14 of these world syringes on weak points in the crust in the early stages of terraforming. They were actually designed to be turned into cities once the planet was stable. Olympus was the first to be inhabited.