Lhotse, (Tibetan: “South Peak”) also called E1, mountain massif in the Himalayas on the border of Nepal and the Tibet Autonomous Region of China. It consists of three summits, the highest of which – Lhotse I at 27,940 feet (8,516 metres) – is the world’s fourth tallest peak.

Lhotse lies just south of Mount Everest, to which it is joined by a ridge at an elevation of about 25,000 feet (7,600 metres). It is sometimes considered part of the Everest massif. E1 was the original survey symbol (denoting Everest 1) for the mountain, which was given to it by the Survey of India (1931). On May 18, 1956, Fritz Luchsinger and Ernest Reiss, two Swiss climbers, made the first ascent of Lhotse I.