Are not my princes altogether kings? One mark of the superiority of Assyria to other countries was to be seen in the fact that her king had not mere officers, but vassal kings under him. Hence the title "king of kings" assumed by so many Assyrian monarchs.
While conquered territories were by degrees and to a certain extent absorbed into the empire and placed under prefects (see the 'Eponym Canon'), an outer zone of more loosely organized dependencies was always maintained by the Assyrians; and these dependencies continued ordinarily to be administered by their native monarchs.
These are the "princes" who were "altogether kings."