Cổ Loa Citadel is a fortified settlement and archaeological site located in northern Vietnam, approximately 17 kilometers north of Hanoi. Situated in the upper plain north of the Red River, the site is significant for its historical role as a potential first political center of Vietnamese civilization.
The citadel is characterized by its unique concentric walls, which are noted for resembling a snail's shell. The settlement featured an outer embankment that covered an area of approximately 600 hectares. Archaeological excavations at the site have uncovered relics belonging to both the Bronze Age Phùng Nguyên culture and the Đông Sơn culture.