The Persian Court
The Great King was the center of court. He was surrounded by an elaborate ritual, which provided him with all the mystery of the oriental potentate. This was a conscious technique of government—a method of structuring charisma into the office and role of kingship so as to enhance the power of the state, and, in part, to protect the function of kingship within the political system from the individual quirks and weaknesses of any given king.
European monarchs of later times often compelled their nobles to be at court, where they could be watched and controlled directly. So also, perhaps, the Great King made court politics of enough importance to limit the autonomy of satraps and other governing officers. When a nobility must spend its time at court husbanding and advancing its political clout, it lacks the time to build strong power bases in the countryside. That such a system sometimes leads to excesses, including murder and violent attempts to grab the throne, does not mean that, in the main, it did not work most of the time as a method of keeping power and the powerful where they could be manipulated by the central authority.
The substantive power of the Persian monarchy lay in its control over patronage and finances. All of the high officers of the court and in the provinces served at the king's will, and most of the bureaucracy down to apparently quite low levels were financially hostage to the royal treasury. Not only did the king do the appointing of high political and military officials, he also fired them frequently. Such regular changes in the upper levels of government prevented opportunities for officials to gather too much power into their own hand by the long-term exercise of a single office. Another form of protection for the government was for the king to appoint his kinsmen to office whenever possible—a good tribal method of rule.
— The Cambridge Ancient History, volume IV, pp. 81-82