The direction your legion is facing is very important. In battle it defines where your formation's front-line is best able to strike or defend its position against an oncoming enemy. Facing away from a proposed attack target reduces effectiveness. Being engaged by an enemy from the side or from behind greatly reduces your legion's ability to defend itself or retaliate; ensuring that casualties taken will be much greater than a legion properly facing its opponent.
Syntax: ... FACE <direction> [CEASE]
Most of the time the direction a legion is facing will either be random (and therefore considered roughly equal in all directions, or consistent with a recent movement) or the result of a set formation (as described above). It is possible, however, to command a legion to remain facing in a specific direction regardless of other considerations. Doing so can be detrimental to the smooth execution of other maneuvers but often keeping one's enemy in line of sight is beneficial, or other times high-tailing it away from an opponent is hastened by resolutely not looking back towards your foe.
NOTE: while executing a change of direction-facing any combat will be less effective, any defences likewise hindered as the formation shifts. If you are attacked in regular melee, the direction facing will be taken into account when evaluating damage taken and likewise when attacking back - consider quite simply if you are flanked you fight at half your effectiveness, if you are ambushed from behind you combat the invasion at one quarter your normal potency. Important battlefield issues, then; the formation and the direction facing.