Maybe. But if you have a canyon, you can use three natural sides, cover the top and one side. The side you can expand as needed. Cities on Earth don't need to

Maybe. But if you have a canyon, you can use three natural sides, cover the top and one side. The side you can expand as needed. Cities on Earth don't need to be protected from toxic soil and hard UV radiation. Instead, most cities on earth have been built near rivers for cheap transportation. Castles and fortifications are built on hills for defensive value.