Visibility

Hills and other terrain features that block line-of-sight can be used to conceal units from the enemy. An army must have line-of-sight to an enemy in order for it to be visible.

Enemy units are also not visible beyond a maximum range, even if there is line of sight.

Seek to control high ground to get an overview of the battlefield.

Flying units can be used to gain line-of-sight to the enemy.

Most units can hide in forests, even within line-of-sight, as long as they are not moving quickly.