Located 16km north of the Old Quarter and dating from the 3rd century BC, Co Loa Citadel was the first fortified citadel in Vietnamese history and became the national capital during the reign of Ngo Quyen (AD 939–44). Only vestiges of the ancient ramparts, which enclosed an area of about 5 sq km, remain.
In the centre of the citadel are temples dedicated to the rule of King An Duong Vuong (257–208 BC), who founded the legendary Thuc dynasty, and his daughter My Nuong (Mi Chau). Legend tells that My Nuong showed her father’s magic crossbow trigger (which made him invincible in battle) to her husband, the son of a Chinese general. He stole it and gave it to his father. With this not-so-secret weapon, the Chinese defeated An Duong Vuong, beginning 1000 years of Chinese occupation.