 The Imbrium Basin is surrounded by three concentric rings of mountains, uplifted by the colossal impact event that excavated it.The outermost ring of mountains has a diameter of 1300 km and is divided into several different ranges; the Montes Carpatus to the south, the Montes Apenninus to the southeast, and the Montes Caucasus to the east.The ring mountains are not as well developed to the north and west, and it appears they were simply not raised as high in these regions by the Imbrium impact.