And at the stream of the brooks that goes down to the dwelling of Ar, and lies upon the border of Moab.
Read Chapter 21
George Leo Haydock
The rocks. Some assert, that the rocks fell upon the enemy: others, that they gave way and opened a passage for the Hebrews, while the rivers were also dried up. Hebrew, "They encamped on the stream of the torrents, which bends towards the dwelling (or city) of Ar, and rests upon the frontiers of Moab. "Thus the book to which Moses alludes, confirms his account of these different encampments. (Calmet)
The Septuagint give rather a different turn of these two verses: "Hence it is said in a book, The war of the Lord has burnt Zoob and the torrents of Arnon
and has sent the torrents to inhabit Er: and it lies upon the borders of Moab. "The river, it seems, had been removed out of its bead by a subterraneous fire or earthquake, and deluged the city of Ar, belonging to Moab. The mighty hand of God terrified those nations, while all nature fought against the wicked and the unwise, Wisdom v. 21. (Haydock)
Rocks were hurled upon the heads of the Amorrhites, and the waters conveyed their dead bodies into the vale of Moab. (Worthington)