[The last situation is not one of the Nine Situations as given in the beginning of chap. XI, but occurs later on (ibid. § 43. q.v.). Chang Yu defines this situation as being situated across the frontier, in hostile territory. Li Ch’uan says it is "country in which there are no springs or wells, flocks or herds, vegetables or firewood;" Chia Lin, "one of gorges, chasms and precipices, without a road by which to advance."] In hemmed-in situations, you must resort to stratagem. In a desperate position, you must fight. 3. There are roads which must not be followed, ["Especially those leading through narrow defiles," says Li Ch’uan, "where an ambush is to be feared."] armies which must be not attacked, [More correctly, perhaps, "there are times when an army must not be attacked." Ch’en Hao says: "When you see your way to obtain a rival advantage, but are powerless to inflict a real defeat, refrain from attacking, for fear of overtaxing your men’s strength."] towns which must not be besieged, [Cf. III. § 4 Ts’ao Kung gives an interesting illustration from his own experience. When invading the territory of Hsu-chou, he ignored the city of Hua-pi, which lay directly in his path, and pressed on into the heart of the country. This excellent strategy was rewarded by the subsequent capture of no fewer than fourteen important district cities. Chang Yu says: "No town should be attacked which, if taken, cannot be held, or if left alone, will not cause any trouble." Hsun Ying, when urged to attack Pi-yang, replied: "The city is small and well-fortified; even if I succeed intaking it, it will be no great feat of arms; whereas if I fail, I shall make myself a laughing-stock." In the seventeenth century, sieges still formed a large proportion of war. It was Turenne who directed attention to the importance of marches, countermarches and manœuvers. He said: "It is a great mistake to waste men in taking a town when the same expenditure of soldiers will gain a province." [1] ] positions which must not be contested, commands of the sovereign which must not be obeyed. [This is a hard saying for the Chinese, with their reverence for authority, and Wei Liao Tzŭ (quoted by Tu Mu) is moved to exclaim: "Weapons are baleful instruments, strife is antagonistic to virtue, a military commander is the negation of civil order!" The unpalatable fact remains, however, that even Imperial wishes must be subordinated to military necessity.] 4. The general who thoroughly understands the advantages that accompany variation of tactics knows how to handle his troops. 5. The general who does not understand these, may be well acquainted with the configuration of the country, yet he will not be able to turn his knowledge to practical account.