It can be inferred from this episode that Ba Sing Se is based on the Byzantine city of Constantinople (now Istanbul). There are many similarities that suggest this. Both Ba Sing Se and Constantinople had large exterior walls that were considered impregnable. Both cities had numerous interior walls. These walls served as both lines of defense and to segregate the population. Both cities had water and farm land inside the walls. This allowed both cities to survive prolonged sieges. In addition to the physical similarities, both cities were the last strongholds of their respective kingdoms. Both cities also fell due to suspected circumstances.