Thus far appointments were held directly from the crown; but beyond this the system was changed.

The ethnic or satrapial commanders appointed the officers next below themselves, the captains over a thousand, and (if their contingent was large enough to admit it) the captains over ten thousand; who, again, nominated their subordinates, commanders of a hundred, and commanders of ten.

Thus, in the main, a decimal scale prevailed.

The lowest rank of officers commanded each ten men, the next lowest a hundred, the next to that a thousand, the next ten thousand.
The officer over ten thousand was sometimes a divisional chief; sometimes he was subject to the commander of an ethnic contingent, who was himself under the orders of the head of a division.

Altogether there were six ranks of officers, exclusive of the commander-in-chief.
The proper position of the commander-in-chief was considered to be the centre of the line of battle.