Jeremiah 49:3 - Matthew Poole's English Annotations on the Holy Bible

Heshbon was formerly a city of the Amorites, of whom Sihon was king, who resided here (but it appears by Jeremiah 49:26 that it was taken from Moab); it is probable that it was at this time a city of Moab: the prophet calls to them to howl for Ai a city of the Ammonites, not the same mentioned Joshua 7:2, for that was on the other side of Jordan. It is uncertain whether by the daughters of Rabbah be to be understood other lesser cities, or the younger women that inhabited Rabbah: he calls to them all to mourn; and for all the indications or signs of mourning, such as girding with sackcloth, running up and down, like persons distracted, by the hedges, where they might be hidden, and not so easily seen. For they shall all go together into captivity; their Melcom, which may signify their idol to whom they gave that name, or their king, or else their supreme magistrate, with their priests and nobles, all orders of persons.