Nanjing has long been one of China's most important cities.[5][6][7] Having been the capital city of six different dynasties since 3 A.D., it is recognized as one of the Four Great Ancient Capitals of China.[8] It was the capital of Wu during the Three Kingdoms Period,[9] and the capital of the Republic of China prior to its flight to Taiwan during the Chinese Civil War.[10] Nanjing is also one of the fifteen sub-provincial cities in the People's Republic of China's administrative structure,