%%Âu Lạc was the nation of the Viet people (between the late third century and 179BC) led by An Dương Vương Thục Phán who had reunified Âu Việt (mountainous regions) and Lạc Việt (lowlands). Âu Việt was also called Tây Âu (ancestors of the Tày, Nùng, Choang at the Sino-Vietnamese frontiers). The Âu Lạc's developement based itself on cultural and economic achievements of Văn Lang in the times of the Hung kings. The agricultural production took the main part. There were great progresses in the military field (arbalests, copper arrows, construction of Cổ Loa Citadel). Âu Lạc fell to Triệu Đà (leader of Nam Việt) in 179BC.