4. 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. 5. If you are anxious to fight, you should not go to meet the invader near a river which he has to cross. 6. Moor your craft higher up than the enemy, and facing the sun. Do not move up-stream to meet the enemy. So much for river warfare. 7. In crossing salt-marshes, your sole concern should be to get over them quickly, without any delay. 8. If forced to fight in a salt-marsh, you should have water and grass near you, and get your back to a clump of trees. So much for operations in salt-marshes. 9. In dry, level country, take up an easily accessible position with rising ground to your right and on your rear, so that the danger may be in front, and safety lie behind. So much for campaigning in flat country. 10. These are the four useful branches of military knowledge which enabled the Yellow Emperor to vanquish four several sovereigns. 11. All armies prefer high ground to low, and sunny places to dark. 12. If you are careful of your men, and camp on hard ground, the army will be free from disease of every kind, and this will spell victory. 13. When you come to a hill or a bank, occupy the sunny side, with the slope on your right rear. Thus you will at once act for the benefit of your soldiers and utilise the natural advantages of the ground. 14. When, in consequence of heavy rains up-country, a river which you wish to ford is swollen and flecked with foam, you must wait until it subsides. 15. Country in which there are precipitous cliffs with torrents running between, deep natural hollows, confined places, tangled thickets, quagmires and crevasses, should be left with all possible speed and not approached. 16. While we keep away from such places, we should get the enemy to approach them; while we face them, we should let the enemy have them on his rear. 17. If in the neighbourhood of your camp there should be any hilly country, ponds surrounded by aquatic grass, hollow basins filled with reeds, or woods with thick undergrowth, they must be carefully routed out and searched; for these are places where men in ambush or insidious spies are likely to be lurking. 18. When the enemy is close at hand and remains quiet, he is relying on the natural strength of his position. 19. When he keeps aloof and tries to provoke a battle, he is anxious for the other side to advance. 20. If his place of encampment is easy of access, he is tendering a bait. 21. Movement amongst the trees of a forest shows that the enemy is advancing. The appearance of a number of screens in the midst of thick grass means that the enemy wants to make us suspicious. 22. The rising of birds in their flight is the sign of an ambuscade. Startled beasts indicate that a sudden attack is coming.