Mare Nubium ("sea of clouds") is a lunar mare in the Nubium basin on the Moon's near side. The mare is located just to the southeast of Oceanus Procellarum. The actual basin is believed to be of Pre-Nectarian system, with the surrounding basin material being of the Lower Imbrian epoch. The mare material is of the Upper Imbrian epoch. The crater to the east of the mare is Bullialdus, which is of the Eratosthenian Epoch. This means the crater is younger than the mare it sits in. The crater that sits on the southern rim of the mare is Pitatus.