From the 8th century BCE to as late as the 2nd century CE an inland trading society emerged on the Xieng Khouang Plateau, near Lao’s most remarkable megalithic remains on a site called the Plain of Jars. The Plain of Jars was nominated to the tentative list as a UNESCO World Heritage Site in 1992, and unexploded ordnance has continued to be removed from the site since 1998. The jars are stone sarcophagi dating from the early Iron Age (500BCE to 800CE) and contained evidence of human remains, burial goods and ceramics. Some sites contain more than 250 individual jars. The tallest jars are more than 3 meters in height. Little is known about the megalithic culture which produced the jars, but the jars and prevalence of iron ore in the region suggest that people who created the site grew wealthy from overland trade routes.