dissected inner region of the Xiangkhoang Plateau in north-central Laos. Drained principally by the Ngum River, a southward-flowing tributary of the Mekong River, the plain is characterized by narrow river valleys and limestone and sandstone hills ranging from 3,000 to 3,600 feet (900 to 1,100 m) in elevation. The plain's name is derived from several hundred huge and ancient carved stone jars that were discovered in the region in the 19th century by the French. In the 1960s the region assumed international strategic importance as a base of operations in the Laotian civil war. Several airfields were established there to support the Laotian government's military operations against Pathet Lao communist insurgents. In 1969 the Plain of Jars was a major battlefield between the North Vietnamese and Royal Lao government and was subjected to heavy bombing by the United States. It is now the site of a major Laotian military airfield. Of little economic or agricultural value, the Plain of Jars has grassy or scrub-covered hills and valleys that support subsistence agriculture by Khmu and Miao (Hmong) peoples.