Giant stone jars of unknown ancient origin are scattered over hundreds of square kilometres around Phonsavan, giving the area the misleading name of Plain of Jars. In fact it's no more of a plain than the rice-bowl valleys at Muang Sing or Luang Namtha, and indeed most of the curious jar sites are on hills. But what is more fascinating than the jars themselves is the mystery of which civilisation created them. Remarkably, nobody knows. But that doesn't stop guides guessing, often amusingly randomly. Meanwhile, a fanciful legend claims that they were made to brew vast quantities of rice wine to celebrate the local people's 6th-century liberation from cruel overlords by the Tai-Lao hero Khun Jeuam. In some versions of this story, the jars were 'cast' from a type of cement made from buffalo skin, sand, water and sugar cane, then fired in 'kilns'. Some even claim that the cave beside Jar Site 1 housed one such kiln. In fact, the jars were fashioned from solid stone and archaeologists estimate they date from the Southeast Asian iron age, between 500 BC and 200AD.
Smaller jars have long since been carted off by collectors but around 2500 larger jars, jar fragments and 'lids' remain. As the region was carpet-bombed throughout the Indochina wars, it's miraculous that so many jars survived. Only a handful of the 90 recorded jar sites have so far been cleared of UXO, and then only within relatively limited areas. These sites, and their access paths, are delineated by easily missed red-and-white marker stones: stay on the white side to avoid a very unpleasant surprise.
Sites 1, 2 and 3 form the bases of most tour loops. Phakeo (a trio of closely linked, overgrown sub-sights) is only accessible by a two-day trek. Although the Plain of Jars is northeastern Laos' most popular tourist attraction, even the main sites are remarkably low-key and can be virtually deserted if you arrive in the afternoon.