When the king of Ai saw it. The particle כְ here employed signifies immediate action. At a time appointed. Or, at the signal. Keil, following Luther, would prefer at the place appointed, which seems to agree best with what follows.
Some copies of the LXX. have ἐπ εὐθείας. Before the plain. Literally, before, or in sight of; i.e; in the direction of the Arabah (see above, Joshua 3:16).