Guangzhou, also known as Canton, is the capital and largest city of Guangdong in southern China. Located on the Pearl River, about 120 kilometres (75 mi) northwest of Hong Kong and 145 kilometres (90 mi) north of Macau, Guangzhou has a history of over 2,200 years and was a major terminus of the Silk Road. The port of Guangzhou serves as a transportation hub. Guangzhou is also one of China's three largest cities. For a long time, it was the only Chinese port accessible to the Europeans. Guangzhou was captured by the British during the First Opium War and no longer enjoyed a monopoly after the war. Consequently, it lost trade to other ports such as Hong Kong and Shanghai, but continued to serve as a major entrepôt at China. Guangzhou is at the center of the Guangdong–Hong Kong–Macau Greater Bay Area, the most populous built-up metropolitan region in the world. The area extends into neighboring cities such as Foshan, Dongguan, Zhongshan, Shenzhen, parts of Jiangmen and Huizhou, as well as Zhuhai and Macau, forming an urban agglomeration of about 70 million residents. It is also part of the Pearl River Delta Economic Zone.