As long as there have been organised armies, there have been military leaders. The Atlanteans were no exception to this, and were typically organised under a Dominate. Whilst we get Dominate from the Latin Dominus, it is believed Latin may have had it's root in the ancient Atlan language, the term Dominate is most likely an example of a loan word. In times of defeat Dominates would surrender their precious horses. 

By the time of Arkantos, Dominates had been phased out for thousands of years - replaced with Admirals due to the Atlantean military becoming secondary to it's navy, on a war of defense. The order was later re-established to lead Kastor's armies, once again bound to a king. Most of these Dominates were officers or noblemen under Arkantos' command and defended many of the Atlantean disphora in the early War of the Titans.