Jaisalmer (jəsälˈmər) [key], former principality, Rajasthan state, NW India. Its terrain is largely a sandy or stony waste and constitutes a section of the Thar Desert. Jaisalmer was brought under the Mughal empire by Akbar in 1570. It became a British protectorate in 1818. In 1949 the region was incorporated into Rajasthan state. The town of Jaisalmer was the capital of the former state. Now a rail terminus and strategic military post close to the Pakistan border, the town is noted for its massive yellow sandstone fort.