Periodizing Sasanian History (224-651 AD) is an important issue in studying the development and change in this important Iranian dynasty. The essential point in this periodization is a focus on legitimization methods and dominant world view in each segment of its history. The present essay will examine the ways in which Sasanian kingship was legitimized and how can this be used in a periodization of the dynasty. By dividing the Sasanian kingship into two early and late (Kayanid) holy kingships based on different methods of legitimization, and further sub-classifications, one can attempt a new periodization. The single previous study of the subject will be critically examined from a theoretical standpoint and social and economic circumstances will be taken into consideration in proposing a new theory.