Phonsavan, population 37,507, is the capital of Xiangkhouang Province. Phonsavan is known for the nearby Plain of Jars, a UNESCO World …Phonsavan, population 37,507, is the capital of Xiangkhouang Province. Phonsavan is known for the nearby Plain of Jars, a UNESCO World Heritage Site. The recorded history of Xiangkhouang is interlinked with the Tai Phuan. The Tai Phuan or Phuan people are a Buddhist Tai-Lao ethnic group that migrated to Laos from southern China and by the 13th century had formed the independent principality of Muang Phuan at the Plain of Jars, with Xiangkhouang as the capital. In the 14th century, Muang Phuan was incorporated into the Lan Xang kingdom under King Fa Ngum.