The Plain of Jars is a large group of historic cultural sites in Laos containing thousands of stone jars, which lie scattered throughout the Xieng Khouang plain in the Laotian Highlands at the northern end of the Annamese Cordillera, the principal mountain range of Indochina. In the context of the Vietnam War and the Secret War, the Plain of Jars typically refers to the entire Xieng Khouang plain rather than the cultural sites themselves.

Archaeologists believe that the jars were used 1,5002,000 years ago, by an ancient Mon-Khmer race whose culture is now totally unknown. Most of the excavated material has been dated to around 500 BC800 AD. Anthropologists and archeologists have theorized that the jars may have been used as funeral urns or perhaps storage for food.

Lao stories and legends claim that there was a race of giants who once inhabited the area. Local legend tells of an ancient king called Khun Cheung, who fought a long, victorious battle against his enemy. He supposedly created the jars to brew and store huge amounts of lao lao rice wine to celebrate his victory.

The first westerner to survey, study and catalogue the Plain of Jars was a French archaeologist, Madeleine Colani of the École française d'Extrême Orient in the 1930s. She excavated the area of jars with her team and found a nearby cave with human remains, including burned bones and ash. Her work is still the most comprehensive although there have been other excavations.

An American bomb damaged the cave during the Vietnam War, when the Pathet Lao used it as a stronghold the surrounding area still has trench systems and bomb craters. The land is littered with metal shrapnel. The town of Xieng Khouang was utterly destroyed during the fighting between the Pathet Lao and American backed anti-communist troops. A new town was built in the mid 1970s, known to foreigners as Phonsavan.