Nanjing (Chinese: 南京; Romanizations: Nánjīng (Pinyin), Nan-ching (Wade-Giles), Nanking (Postal map spelling)) is the capital of China's Jiangsu Province and a city with a prominent place in Chinese history and culture. Nanjing served as the capital of China during several historical periods, and is listed as one of the Four Great Ancient Capitals of China. Nanjing is also one of the fifteen sub-provincial cities in the People's Republic of China's administrative structure, enjoying jurisdictional and economic autonomy only slightly less than that of a province. In addition, the Republic of China claims it as its de jure capital. Located in the downstream Yangtze River drainage basin and Yangtze River Delta economic zone, Nanjing has always been one of China's most important cities. Apart from having been the capital of China for six dynasties and of the Republic of China, Nanjing has also served as a national hub of education, research, transportation and tourism throughout history. With an urban population of over five million, it is also the second largest commercial center in the East China region, behind only Shanghai.