Either,
1. Before the ark, by which they, as well as the rest, passed when they went over Jordan. Or,
2. In the presence of God, who diligently observed whether they would keep their promise and covenant made with their brethren, or not.
Related Commentaries of Joshua 4:13
Joshua 4:13
13 About forty thousand prepareda for war passed over before the LORD unto battle, to the plains of Jericho.