prepare ditch and fosse
reconnoiter field of battle
assume tactical formation: column, line, closed, extended, etc..
some of these could be simple modifiers, perhaps preparing your camp
before the battle aids in defense strength, etc.., and these skills might
require certain kinds of people, like workers to raise a mound, or advanced
warriors to recon the potential field of battle ahead of time. Again,
certain tactical formations might require certain types of troops. For
instance, it's only realistic to think of a phalanx in terms of pikemen.