When an invading force crosses a river in its onward march, do not advance to meet it in midstream. It will be best to let half the army get across, and then deliver your attack. 438

If you are anxious to fight, you should not go to meet the invader near a river which he has to cross. 439

Moor your craft higher up than the enemy, and facing the sun. 440 Do not move upstream to meet the enemy. 441 So much for river warfare.

In crossing salt-marshes, your sole concern should be to get over them quickly, without any delay. 442