Albert Barnes Commentary Joshua 8:14

"And it came to pass, when the king of Ai saw it, that they hasted and rose up early, and the men of the city went out against Israel to battle, he and all his people, at the time appointed, before the Arabah; but he knew not that there was an ambush against him behind the city." — Joshua 8:14 (ASV)

At a time appointed - Rather, at the place appointed, that is, some spot suitable for the drawing up of his men, which had been assigned beforehand. This was before the plain, that is, it was at the entrance of the depressed tract of land which runs down to the Jordan valley, up which lay the route of the Israelites from Gilgal to Ai.