Cổ Lóa

Cổ Loa Citadel is an ancient fortified city and archaeological site in present-day Hanoi's Đông Anh District, roughly 17 kilometers north of Hanoi, in the upper plain north of the Red River. Relics of the Bronze Age Phùng Nguyên culture and Đông Sơn culture have been found in Cổ Loa. It might be the first political center of the Vietnamese civilization. The settlement’s concentric walls resemble a snail’s shell; it had an outer embankment covering 600 hectares.

From the Wikipedia article Citadel of Cổ Loa, CC BY-SA 4.0.