And when they had set. This may mean the leaders of the detachment of 30,000. Joshua does not appear to have been with them, for he is not mentioned till the latter part of the verse (see note on verse 3).
Joshua went that night. Having made all his dispositions, he descended in the evening from his vantage ground on the hill into the plain, so as to invite attack in the morning, a stratagem which (see next verse) was completely successful.
Some MSS; however, have וַיָּלֶן "and he rested," for וַיֵּלֶךְ"and he went" here. The valley. The word here is עֶמֶק not גָי as in verse 11. Therefore the narrow waterless ravine in which the troops in ambush were to lie hid is not meant here, but a wider valley.
A consideration of this fact might do something to settle the much disputed question of the situation of Ai. The עֶמֶק though deep, as the name implies, was a valley large enough for cultivation or luxuriant vegetation (Job 39:10; Ps 65:14; So Psalms 2:1).
Even a battle might be fought there (Job 39:21). Such a valley as that of Chamonix or Lauterbrunnen would answer to the description, and so would the passes of Glencoe and Killiecrankie.