Changing Capitals and Canal Course: Xi’an and Luoyang

Six out of the top 10 most attractive tourist sites during the 5-day Labor Day holiday in China were historical sites. Three are in Beijing - the Great Wall, the Summer Palace and Yuanmingyuan, or Old Summer Palace. The other three are the Longmen Grottoes in the ancient city of Luoyang in central China, the Ming Dynasty city wall in Xi’an in China’s northwest and the Humble Administrator’s Garden, or Zhuozhengyuan in Suzhou, Jiangsu Province, in China’s east. 
 Beijing, Luoyang and Xi’an have something in common – they are all famous for their long history as dynastic capitals. If we add up the length of time Chinese cities served as a capital to different dynasties, Luoyang comes out top, followed by Xi’an and Beijing. Luoyang and Xi’an lost their glory as capitals more than 1,000 years ago.  
How did Luoyang and Xi’an rise to dominate as choices for dynastic capitals? And what prompted their decline? Changes in environment, especially water resources, is a major reason.