The present-day Sherpas are the descendants of a small group of families who emigrated from the Khams region of Tibet across the Himalayan range in the middle of the sixteenth century under the leadership of a great lama, or religious preceptor. The valleys into which they moved appear to have been sparsely settled at the time of their arrival. They lived by raising field crops in the cleared forest land and herding livestock, including yaks, cows, and yak-cow crossbreeds, prized for their excellent milk, in the higher pastures. During the nineteenth century, under the aegis of the British Raj in India and the Rana dynasty in Nepal, some Sherpas took advantage of their location near the Nana pa La, or "Inside Pass" Between Tibet and Nepal, to establish themselves as intermediaries in trade routes linking China and the Indian subcontinent, using the yak as a transport animal ideally suited to alpine caravans. The introduction of the Irish potato into the region in the middle of the nineteenth century added prosperity to the region: this allowed for denser settlements in the high villages of Khumbu above the tree line but near the pass and the yak pastures. The potato is now the main staple crop of the Sherpas; before its introduction, they subsisted on grain, especially barley, and dairy products. In the years following the opening of Nepal to the west, after the restoration of the Shaha monarchy in 1952, mountaineering and tourism became major industries. Sherpas from Darjeeling had already established a reputation as able assistants on British surveying and mountaineering expeditions by the beginning of the century. The conquest of Mount Everest (in Nepali, Sagarmatha; in Sherpa, Chomolungma) in 1953 by a British team relying on Sherpa porters and guides—with a Sherpa climber, Tenzing Norgay, as one of the first two people on the summit, along with Sir Edmund Hillary—brought the Sherpas worldwide attention. Since then, work related to the tourist, trekking, and mountaineering trade has more and more dominated the economy of the Sherpas, who serve as guides, sirdars (expedition foremen), and service providers in the cash economy of tourism. The Sherpas in the towns, especially Darjeeling, are drawn there by wage labor in industries such as road building and tea planting. A few Sherpas made great fortunes as road-building labor contractors under the British and more recently since Indian independence. Although the Nang pa La is no longer an active trade route, trading, both within the region and over long distances throughout much of Asia, is an important Sherpa economic activity.