The formation of Tianjin has undergone a long period of time. The name of Tianjin, first emerged during the early period of Emperor Yongle of China's Ming Dynasty, means a ferry crossing where the Son of Heaven has passed. In the second year of Emperor Yongle of the Ming Dynasty (1404), Tianjin started building fortifications and defenses as a strategic military place. In 1860 Tianjin was turned into an open port. For years its industrial production and port trade volume were only second to Shanghai, becoming the second largest commercial city in China and the biggest financial and trading center in north China. After the founding of the People's Republic of China Tianjin was turned into a municipality directly under the central authorities.