天陷, explained as 卑下汙𣾈車騎不通 “low-lying places, so heavy with mud as to be impassible for chariots and horsemen.” and crevasses, 天隙 is explained by Mei Yao-ch‘ên as 兩山相向洞道狹惡 “a narrow difficult way between beetling cliffs,” but Ts‘ao Kung says 山澗迫狹地形深數尺長數丈者, which seems to denote something on a much smaller scale. Tu Mu’s note is 地多溝坑坎陷木石 “ground covered with trees and rocks, and intersected by numerous ravines and pitfalls.” This is very vague, but Chia Lin explains it clearly enough as a defile or narrow pass: 兩邊險絶形狹長而數里, and Chang Yü takes much the same view. On the whole, the weight of the commentators certainly inclines to the rendering “defile”. But the ordinary meaning of 隙 (a crack or fissure) and the fact that 絶澗 above must be something in the nature of a defile, make me think that Sun Tzŭ is here speaking of crevasses. The _T‘ung Tien_ and _Yü Lan_ read 郄 for 隙, with the same meaning; the latter also has 大害 after 天郄—a palpable gloss. should be left with all possible speed and not approached. 16. 吾遠之敵近之吾迎之敵背之 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. 軍旁有險阻蔣潢井生葭葦小林蘙薈必謹覆索之此伏姦之所藏處也 If in the neighbourhood of your camp The original text has 軍行, but 旁 has been generally adopted as yielding much better sense. there should be any hilly country, 險阻 is 邱阜之地, according to Chang Yü. ponds surrounded by aquatic grass, hollow basins filled with reeds, The original text omits 蔣 and 生, so that 潢 and 井 join to make a pair: “ponds and basins.” This is plausible enough at first sight, but there are several objections to the reading: (1) 蔣 is unlikely to have got into the text as a gloss on 潢; (2) it is easy to suppose, on the other hand, that 蔣 and afterwards 生 (to restore the balance of the sentence) were omitted by a copyist who jumped to the conclusion that 潢 and 井 must go together; (3) the sense, when one comes to consider it, actually requires 蔣, for it is absurd to talk of pools and ponds as in themselves suitable places for an ambush; (4) Li Ching (571–649 A. D.) in his 兵法 “Art of War” has the words: 蔣潢蘙薈則必索其伏. This is evidently a reminiscence of Sun Tzŭ, so there can be little doubt that 蔣 stood in the text at this early date. It may be added that the _T‘ung Tien_ and _Yü Lan_ both have 蔣, and the latter also reads 并 for 井. or woods with thick undergrowth, I read 小林 with the _Yü Lan_ in preference to 山林, given in the original text, which is accepted by the commentators without question. The text of the _T‘u Shu_ up to this point runs as follows: 潢井蒹葭林木蘙薈者. they must be carefully routed out and searched; for these are places where men in ambush or insidious spies are likely to be lurking.