a comparison of the principles of legitimacy in achaemenid and sassanid's states

since the beginning of human history, one of the basic dilemmas that every political institution must solve is how to exercise legitimate authority- that is, how to govern with the consent. “you can’t sit on bayonets,” goes an old political expression. this is a way of saying that although a state can exercise its power through the use of police force or coercion, in the long run the use of force will not be sufficient to govern a society. for political sociologists since weber’s time, the answer to this question begins with the concept of legitimacy. according to discussions  considered in this paper, and historical review of two systems- achaemenid and sassanid- we can conclude that thought in iranian social from achaemenid to sassanid was evolving and according to weber's idea, although legal authority is for modern society,  the thought that political authority comes ‘from below’ and the concept of social contract  existed in ancient iran.