Jamieson, Fausset and Brown on Joshua 6:17-19

17-19. And the city shall be accursed--(See on Le 27:28). The cherem, or "anathema," was a devotion to utter destruction (De 7:2; 20:17; 1Sa 15:3). When such a ban was pronounced against a hostile city, the men and animals were killed--no booty was allowed to be taken. The idols and all the precious ornaments on them were to be burned (De 7:25; compare 1Ch 14:12). Everything was either to be destroyed or consecrated to the sanctuary. Joshua pronounced this ban on Jericho, a great and wealthy city, evidently by divine direction. The severity of the doom, accordant with the requirements of a law which was holy, just, and good, was justified, not only by the fact of its inhabitants being part of a race who had filled up their iniquities, but by their resisting the light of the recent astonishing miracle at the Jordan. Besides, as Jericho seems to have been defended by reinforcements from all the country (Jos 24:11), its destruction would paralyze all the rest of the devoted people, and thus tend to facilitate the conquest of the land; showing, as so astounding a military miracle did, that it was done, not by man, but by the power and through the anger, of God.