This essay discusses the importance of Ctesiphon in the historical and literary tradition of Sasanian and Post-Sasanian Iran. It is proposed that there was a significant buildup of the Ctesiphon’s defenses in the third century that it made its conquest by the Roman Empire impossible and its gave it an aura of impregnability. By the last Sasanian period the city was not only inhabited by Iranian speaking people and a capital, but it also became part of Iranian lore and tradition, tied to mythical Iranian culture-heroes and kings. Even with the fall of the Sasanian Empire, in Arabic and Persian poetry the grandeur and memory of Ctesiphon was preserved as part of memory of the great empires of the past.