At that time, the enemy troops along the southeast coast retreated to the sea under the attack of Qi Jiguang and other Ming troops, and did not dare to harass again in a short time. When the imperial court saw that the Japanese invaders were wiped out, it focused on the defense in the north.
By 1567, Mongolian tribal leader An Dan led Mongolian cavalry and invaded the Great Wall such as Shanhaiguan many times. Mongolian cavalry often went to Jizhou, Changli, Funing, Laoting, Lulong and other places to rob local people of food and property. The people were very afraid, and their lives and property suffered serious losses. The border situation is very serious.
Seeing the deterioration of the situation, the court urgently discussed countermeasures, so it dispatched Tan Lun, Governor of Guangdong and Guangxi, Qi Jiguang, Company Commander of Fujian, and Yu, Company Commander of Guangxi, to the north to rectify the border defense.
1569, Qi Jiguang was appointed as the company commander of Jizhou town, guarding Jizhou, Yongping and Shanhaiguan. His view of Mongolian cavalry is: "The only way to stop its long drive is to station troops and take side walls to prevent them from coming and going."
Qi Jiguang saw that the Great Wall guards were weak and the fighting capacity was low, so he first transferred his former subordinates to the outskirts of Miyun for standby, and then enriched the Shanhaiguan defense line. Subsequently, more than 20,000 southern soldiers moved one after another, enriching the defense of Shanhaiguan.
Qi Jiguang is a man of perseverance. He constantly strengthened training, improved weapons, and built walls to stop Mongolian cavalry.
Qi Jiguang applied his experience of the Anti-Japanese War in Taizhou to this place and built a large number of hollow enemy platforms on the Great Wall. He took great pains to personally draw up the rules for building enemy platforms, and improved and innovated them on the basis of building enemy platforms in Taizhou. At 158 1, 1448, a hollow enemy platform was built where he defended, which could be attacked and retreated.
Qi Jiguang thinks that the Great Wall is not strong enough. Referring to Taizhou's experience in building a solid wall with masonry on both sides, he used masonry to build the Great Wall on a large scale, that is, on the basis of trimmed stone strips, the wall was built with blue bricks inside and outside to the top, and the interior was jointed with white mortar and concrete to ensure that the wall was solid and durable.
At the same time, he perfected the ancillary facilities of the Great Wall and built many additional facilities such as crib walls and hanging eyes. Cut slopes, dig ditches and dig pits outside the wall to weaken the enemy's attack ability.
Through these measures, a complete and solid fortification system has been formed, with high walls and numerous enemy stations facing each other.
The eastern starting point of this fortification is called Laolongtou, which is 4 kilometers south of Shanhaiguan. The Great Wall of the Ming Dynasty spanned the mountains and extended to the Bohai Sea like a dragon, so this place was called the "Old Dragon Head". The old faucet consists of Shicheng, Jinglutai, Nanhai Kouguan and Chenghailou.
It is said that the Old Dragon Head Haishishi Town was built by Qi Jiguang to prevent Mongolian cavalry from sneaking into the seaside at low tide or in winter dry season.