Besides the royal family itself--or clan of the Achaemenidae--there were six great houses which had a rank superior to that of all the other grandees.

According to Herodotus these houses derived their special dignity from the accident that their heads had been fellow-conspirators with Darius Hystaspis; but there is reason to suspect that the rank of the families was precedent to the conspiracy in question, certain families conspiring because they were great, and not becoming great because they conspired.

At any rate, from the time of Darius I., there seem to have been seven great families, including that of the Achaemenidae, whose chiefs had the privilege of free communication with the monarch, and from which he was legally bound to choose his legitimate wives.

The chiefs appear to have been known as "the Seven Princes," or "the Seven Counsellors," of the king.

They sat next to him at public festivals; they were privileged to tender him their advice, whenever they pleased; they recommended important measures of state, and were, in part, responsible for them; they could demand admission to the monarch's presence at any time, unless he were in the female apartments; they had precedence on all great occasions of ceremony, and enjoyed a rank altogether independent of office.