The Plain of Jars is a megalithic archaeological landscape in Laos. It consists of thousands of stone jars scattered around the upland valleys and the lower foothills of the central plain of the Xiangkhoang Plateau. Between 1964 and 1973, the Plain of Jars was heavily bombed by the US Air Force during a period of the Second Indochina War (1955-1975) known as the by-proxy Secret War operating against North Vietnamese and Pathet Lao communist forces. The US Air Force dropped more bombs on Laos, primarily the Plain of Jars, than it dropped during the whole of World War II. This included 262 million anti-personnel cluster bombs. An estimated 80 million of these did not explode and remain a deadly threat to the population.