In brief
Bam's fortress architecture is associated with an oasis and an underground water supply. The walls do not explain the existence of the city themselves.
Useful to know
Bam is located in a desert environment in Iran. UNESCO connects the life of the oasis with the underground water channels kanati and describes Arg-e Bam as a representative fortified city built with traditional earth techniques. [1]
For architectural reading, the water supply is as essential as the visible fort. If you only look at the fortress silhouette, you miss the infrastructure that allows for habitation of the place.
A useful task is to allocate to a scheme the protection, living spaces and water supply. The scheme can be simplified, but it should not mix the channels with streets or come up with accurate routes without a source.
The historical description of the Earth's city is not an estimate of the current preservation of each wall. For a specific photo, check when it was taken and what its context is before using it as evidence of the condition of the entire ensemble.
Sources
For further detail and to check the information: