Nanjing is one of oldest cities and constructed as early as 472 B.C, Nanjing is rich in culture but also modern and exciting. Located in the lower Yangtze River drainage basin and Yangtze River Delta economic zone, Nanjing has long been one of China's most important cities. 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. It was the capital of Wu during the Three Kingdoms Period, and the capital of the Republic of China prior to its flight to Taiwan during the Chinese Civil War. 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. Nanjing has long been a national centre of education, research, transport networks and tourism. It was the host city of the 2014 Summer Youth Olympics.