Then too there are oligarchies whose fall is due to the extravagant living of their members. For persons of this type seek to make innovations, either aiming at tyranny themselves or putting up some other person [a close relative perhaps]…at Aegina the person who had carried through the negotiations with Chares tried to change the constitution because he had no money left. Sometimes they do not wait for the money to run out but begin by making changes. Sometimes they secretly help themselves to public funds; and then, either they themselves stir up strife in order to conceal their embezzlement, or else others do so in order to call attention to it, as happened at Apollonia on the Black Sea.
An oligarchy which is of one mind with itself is not easily destroyed from within; a good example is the constitution at Pharsalus, where a few men continue to have authority over many simply because they know how to treat each other properly. But if an attempt is made to set up one oligarchy within another, its dissolution follows. This occurs whenever, with a total citizen-body that is not large, not all the few are eligible for the highest offices. It happened in Elis, where the constitution was oligarchical but very few persons were ever even added to the governing body or council of elders, because the existing members held office for life and the total was fixed at ninety; moreover the method of election favoured the group in power, like that of the Spartan Council of Elders.
Aristotle, The Politics, 1962, London: Penguin Books, pp 203-4