The Art of War by active 6th century B.C. Sunzi

9. In dry, level country, take up an easily accessible position with

rising ground to your right and on your rear, [Tu Mu quotes T’ai Kung as saying: "An army should have a stream or a marsh on its left, and a hill or tumulus on its right."] so that the danger may be in front, and safety lie behind. So much for campaigning in flat country.