Hanoi is the capital and second-most populous city of Vietnam. It covers an area of 3,359.82 km2, and consists of 12 urban districts, one district-level town and 17 rural districts. It is located within the Red River Delta of Northern Vietnam. Hanoi's history goes back to the third century BCE, when a portion of the modern-day city served as the capital of the historic Vietnamese nation of Âu Lạc. Following the collapse of Âu Lạc, the city was part of Han China.