After Zhu Yuanzhang, the founding emperor of the Ming Dynasty, ascended the throne, he divided his sons into kings and stationed them all over the country. His fourth son, Judy, was made a prince and stationed in Peiping, which is now Beijing. After Zhu Yuanzhang's death, he passed it on to his eldest grandson Zhu Yun. In order to compete with Zhu Yun for the throne, Judy launched the "Battle of Jingnan" in the history of China. 1399, Judy, the prince of Yan, led his army south, crossed the river from Sanchakou, Tianjin, and attacked Cangzhou. 1402, invaded Nanjing, the capital of the Ming dynasty, and ascended the throne of the emperor. After Judy acceded to the throne, she admired the Sanchahekou he passed when he fought in the world. He thought it was a treasure trove of geomantic omen and asked his minister to give them names. Finally, Judy chose the word "Tianjin", which means "the son of heaven crossed the land of Tianjin", hence the name Tianjin. Soon, Judy moved to Beijing, Tianjin became the gateway of Beijing, and its military status became increasingly important. In the second year of Yongle in the Ming Dynasty (AD 1404), Wei was established in Tianjin. Wei was the military establishment of the Ming Dynasty, and Tianjin * * * set up three guards with more than 16,000 troops. Therefore, people also call Tianjin Tianjinwei. Building a city is building a city, and Tianjin, as a complete urban history, started from here.