The name ymbryum comes from the latin name Mare Imbrium. To be more specific about the mare, it is a large basaltic plain on the Earth's Moon. The maria (Latin for "seas") were so dubbed by early astronomers who mistook them for actual seas. The largest of the lunar maria, Mare Imbrium sits in the Imbrium basin. The basin material is of the Lower Imbrian epoch, with the mare material being of the Upper Imbrian and Eratosthenian epoch. 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 southwest, and the Montes Caucasus to the east.