Located by King An Duong in the area of Co Loa, about 16 km north of Hanoi city, Veitnam, Co Loa was chosen to be the capital of the state of Au Lac, which was established along the Red River Delta.

This state was originally founded after the Tay Au conquest of the Hung kings of Van Lang in 258 BC. Covered a large area of more than five square km, the Co Loa citadel is originally constructed with the walls arranged in a spiral shape that consists of nine coils.