Heshbon was formerly the city of Sihon, Numbers 21:26; it became afterward one of the principal cities of the Moabites, as appeareth from Isaiah 15:4; which maketh the learned author of our English Annotations think our translation not so good; for why should they devise evil in Heshbon against Moab, unless the enemies sat there in council, when they had taken it, against the other parts of the country? But possibly the sense is, they shall no more in Heshbon magnify Moab, or Moab shall no more glory of Heshbon, for the enemies had contrived the ruin of it. Madmen was another city in the country of Moab. Some think the same with Ptolemy's Madiama. To that city also the prophet threateneth ruin and destruction by the sword.
Related Commentaries of Jeremiah 48:2
Jeremiah 48:2
2 There shall be no more praise of Moab: in Heshbon they have devised evil against it; come, and let us cut it off from being a nation. Also thou shalt be cut down, O Madmen; the sword shall pursue thee.