Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Take you twelve men - The order is given in the plural, because no doubt the tribes themselves were to choose their own representatives, the choice being approved by Joshua Jos 4:4. These twelve would be left with Joshua on the hither bank of the river, waiting to receive his orders after the rest of the people had made their way across Jos 3:17; Jos 4:1.
Laid them down there - i. e. in Gilgal Jos 4:20. Spoken of as the doers of this, because it was done by the twelve who acted for them.
Another set of stones is intended than that before mentioned. The one set was erected by the command of God at the spot where they passed the night Jos 4:3; the other by Joshua on the spot where the priests' feet rested while they bore up the ark during the passage of the people. This spot was near, or perhaps on, the eastern brink (compare Jos 3:8). These stones would therefore mark the spot at which the people crossed, as the others marked the place in which they lodged the night after the crossing; nor, as the stones would only be reached by the water in flood time, and then by the utmost edge of it, is there any reason why they could not both be seen, and continue in their place as the writer asserts they did up to the time when he wrote.
The plains of Jericho, consisting of the higher terrace of the Jordan valley, are almost seven miles broad. The mountains of Judaea here recede somewhat from the river, and leave a level and fertile space, which, at the time of Joshua's invasion, was principally occupied by a forest of palms. Hence, the name "city of palms," Deu 34:3.
The passage of the priests to the further bank had been already referred to, Jos 4:11; but the writer, in observance of his general plan (compare introductory remarks to Josh. 3), re-introduces it here as the leading feature in the concluding section of his account, and (as before) with mention of God's special direction about it. The statement that on the removal of the ark the waters of Jordan at once returned to their former level Jos 4:18, heightens the impression which is especially inculcated throughout - that the whole transaction was extraordinary and miraculous. The details and incidents of the passage are no doubt open to manifold discussion: but all such discussion will be futile unless it proceed throughout on the admission that we have here before us the record of a distinctly supernatural interposition: compare the introduction to the Book of Joshua.
Gilgal, mentioned here by anticipation (compare Jos 5:9), the modern Jiljulieh (Conder), was on rising ground (compare Jos 5:3), and, according to Josephus, nearly five miles from the river, and consequently about two from the city itself. The site of the camp was no doubt fortified by Joshua, as it constituted for some time the abiding foothold in Canaan, from where he sallied forth to subdue the country. It was also the place of safety where the ark, and no doubt also the women, children, cattle, and other property of the people were left. Hence, the demolition of Jericho and Ai, strong fortresses in the neighborhood of Gilgal, was no doubt dictated by sound policy as well as by religious obligations.