The how and why of Tehran development and construction of its Citadel has always been of interest to researchers. At the same time, Issues such as its time of obtaining importance and prosperity on the one hand, and establishing and appellation of its Citadel as the most important official complex of the Qajar period on the other, are among the concerns mostly ignored by the scholars. Addressing the above- raised questions, the present study has been analyzing the development time of the city as well as construction and name of its Citadel by checking reliable historical references and also scrutinizing the related assumptions regarding them.