The city of Beijing has a long and rich history that dates back over 3,000 years. Before the unification of China by the First Emperor in 221 BC, Beijing had been for centuries the capital of the ancient states of Ji and Yan. It was a provincial center in the earliest unified empires of China, Qin and Han. The northern border of ancient China ran close to the present city of Beijing, and northern nomadic tribes frequently broke in from across the border. Thus, the area that was to become Beijing emerged as an important strategic and local political center.

Source: Wikipedia