The legion exercise sand table is extremely detailed; the Legion Leader can even micro-manage at the war camp level. Of course, under normal circumstances, the Legion Leader wouldn't engage in such micro-management.
A legion can consist of more than fifty thousand people, with a vast defense area, and just managing the overall situation is enough to give the Legion Leader a headache.
Of course, since the sand table was manufactured during the Divine Martial Era, the legion's organization is naturally also based on the standards of the Divine Martial Era.
Fortunately, the military structure of the Immortal Dynasty is also based on that of the Divine Martial Era. A fully-staffed legion consists of about fifty to sixty thousand people, with nine to ten battalions, and a total of over a hundred war camps, making it fairly easy to command.
