The "Treatise on Geography" in the Old Book of Tang recorded: Taiyuan, Tang's northern capital, was where Emperor Gaozu raised his army. Later generations regarded it as the lock and key of the northern gate.
On the twenty-eighth day of the first month of Jinghe Year Sixteen, snow weighed down the Yan Mountains.
The Northern Capital stood higher than the Southern Capital, its walls were thicker, and its winds harsher.
This city had been founded when Great Zhou's Emperor Taizu marched north against Khitan.
Emperor Taizu proclaimed himself emperor in the Southern Capital, but established a smaller administration in the Northern Capital: not all Six Ministries were present, only the three departments of War, Works, and Revenue.
Nor was there a full complement of court officials, merely a resident administrator and several advisers.
Emperor Taizu said, "The Southern Capital is the heart; the Northern Capital is the wall. The heart must not move, and the wall must not fall."
Every subsequent sovereign of Great Zhou resided in the Southern Capital.
Yet whenever trouble arose in the north, the Northern Capital became the temporary imperial seat.
When Emperor Shizong repelled Khitan three times, he stationed himself in the Northern Capital, leaving the Crown Prince-the present Emperor Jing of Zhou-in the Southern Capital with orders to govern as regent.
In peaceful years, when there was no war, the Northern Capital became a place where feudal princes took up their fiefs.
Such was Great Zhou's established rule.
Whenever a new sovereign ascended the throne, he would enfeoff his most trusted brother as Prince of Yan and send him to the Northern Capital to guard this northern wall for Great Zhou.
During the Emperor Shizong Era, the Prince of Yan was Emperor Shizong's younger brother.
In Emperor Jing's reign, the Prince of Yan