--祖冲之--

The Han Dynasty lasted for 427 years from 206 BC to 220 AD. When it fell, the Three Kingdoms period took its place as local power centers established their own dynasties. They were reunited to form the Jin Dynasty (晋 264 to 420) which lasted 157 years in various forms. The Jin Dynasty was under constant attack from the north as the Xiongnu culture of the northern plains moved south followed by the Jie and the Xianbei. Each were distinct cultures that brought not only war and destruction but new ideas and practices.
~ During and after the Jin Dynasty there was a massive movement of population to the south of the Yangtse River for safety. The Jin Dynasty broke up into small kingdoms. This is called the Sixteen Kingdoms period (五 胡 十 六 国 (304 to 439) and overlaps the establishment of the five Northern and four Southern Dynasties (南 北 朝 386 to 589). The Southern Dynasties had their capitals south of the Yangtse River in Nanjing. The four Southern Dynasties were: Liú-Sòng 刘宋 420-479, Southern Qí 南齐 479-502, Liáng 南梁 502-557, and Chén 南陳 557-589.
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~http://hua.umf.maine.edu/China/astronomy/tianpage/0014ZuChongzhi9296bw.html
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