After crossing a river, you should get far away from it.

When an invading force crosses a river in its onward march, do not advance to meet it in mid-stream. It will be best to let half the army get across, and then deliver your attack. If you are anxious to fight, you should not go to meet the invader near a river which he has to cross.

Moor your crafter higher up than the enemy, and facing the sun. Do no move up-stream to meet the enemy. So much for river warfare.

–Sun Tzu, The Art of War, Chapter IX: The Army on The March, [3-6].

Here are some general questions to ask when you see a river on the tabletop:

  1. Can the river be crossed at a certain point (bridge, ford, etc.) without a penalty to movement?
  2. Do you know, before the game starts, where you can cross the river? Some scenarios may require that you scout out fords, which can waste a lot of time.
  3. Do these crossing points serve as “choke” points on the battlefield? Such as when a river runs down the center of the tabletop and there’s only one bridge.
  4. Can you anchor a flank to a river? During the Seven Years’ War, this is Frederick the Great often did.
  5. What is exactly the movement penalty to crossing a river? Some rule sets are vague as to when units take this penalty. If there’s a house rules, make sure you know it.
  6. Can you attack your opponent’s forces as they cross the river? Many rules set have units become “disordered” as they cross a river. Take advantage of this, as per Sun Tzu’s advice.
  7. Do you have to cross a river to reach your objectives? Or more than one river?

Just one river can slow you down. Two or more rivers can make your objectives impossible to achieve. You might want to reconsider playing the scenario if somebody has laid out an “obstacle course” for you.

Next on The Art of Wargaming:

The Sinister Secret of Saltmarshes.