The early years of the eighteenth century were a period of acute political instability throughout Nam Việt. During this time the north west was overrun by armies belonging to the Phẻ, a branch of Tày-Thái-speaking people from southern Yunnan Province who ousted the Lừ ruling family from Mường Thanh and proceeded to commit unspeakable acts of barbarism against the inhabitants of the area. However, in 1754 a Vietnamese peasant leader from the Red River Delta named Hoàng Công Chất, whose army had retreated into the region to escape from royal troops, rallied local Lừ, Lào and Thái chieftains to his support and expelled the Phẻ back across the border to China. Building a fortress at Bản Phủ, Chất subsequently set himself up as lord of a large area of north west Việt Nam which incorporated not only modern Sơn La, Điện Biên Phủ and Lai Châu provinces but also large tracts of Hòa Bình, Thanh Hóa, Vĩnh Phúc and Lào Cai. Over the next decade Chất is said to have won the hearts of all the local people by carrying out important land and taxation reforms. After Chất's death in 1767 his son Hoàng Công Toan briefly assumed the title Quốc Công or ‘Great Duke’, but was ultimately driven out by royal armies. Nonetheless, the exploits of Hoàng Công Chất still live on today in the songs and stories of the ethnic people in and around Điện Biên Phủ. The remnants of Chất's citadel and a temple erected in his memory may be visited at Bản Phủ, some 10 kilometres south west of Điện Biên Phủ in the direction of the Lao border. While little now remains of the fortress itself, the temple contains a small display of historic relics excavated from the Bản Phủ citadel area, including a wine cup, arrows and spear and axe heads. On the wall are a map of Hoàng Công Chất's military campaigns and a plan of the immediate area, which gives the following information about his citadel: 'Construction of Bản Phủ citadel commenced in 1758 and was completed in 1762. The citadel was 80 mẫu (1 mẫu = 3.6 square metres) wide, the road into the citadel 4,000 metres long and 10 metres wide and the front wall of the citadel 5 metres wide x 5 metres high. Around the citadel was planted a large forest of 30,000 bamboo trees. Outside the bamboo forest was a moat 5-metres deep and 10 metres wide. The citadel was divided into two areas - the inner city comprised the officers’ quarters, the outer area had a drill yard, a storehouse and a general army barracks. Hoàng Công Chất had 133 ponds dug to cater for the daily drinking water and cooking needs of the insurgents, using the excess earth to fortify the walls of the citadel.'