Charles Ellicott Commentary Joshua 8:13

"So they set the people, even all the host that was on the north of the city, and their liers-in-wait that were on the west of the city; and Joshua went that night into the midst of the valley." — Joshua 8:13 (ASV)

Joshua went that night into the... valley (Emek). —Not the ravine (or Gai) previously mentioned (Joshua 8:11), but a wider and more open part of the valley, probably a little further to the south; the object being to draw the men of Ai into a pursuit in the direction of the road to Gilgal.