By the waters of Merom suddenly - Joshua, being apprised of this grand confederation, lost no time, but marched to meet them; and before they could have supposed him at hand, fell suddenly upon them, and put them to the rout.
Suddenly - As before, at Gibeon Joshua 10:9, so now Joshua anticipates his enemies. Taken by surprise, and hemmed in between the mountains and the lake, the chariots and horses would have no time to deploy and no room to act effectively; and thus, in all probability, the unwieldy host of the Canaanites fell at once into hopeless confusion.