天牢 “natural pens or prisons,” explained as 三面環絶易入難出 “places surrounded by precipices on three sides — easy to get into, but hard to get out of.”
天羅, explained as 草木蒙密鋒鏑莫施 “places covered with such dense undergrowth that spears cannot be used.”
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.”
天𨻶 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 𨻶 (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 𨻶, 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. 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
The original text has 軍行, but 旁 has been generally adopted as yielding much better sense.