Border Defence As Well As Its Gain And Loss Of Northwest Border Towns In Ming Dynasty

In Ming dynasty, northwest border refer to the four borer towns,they were Yansui,Ningxia,Gansu,Guyuan,which lie in northwest.they had special function and outstanding position in ming's national defense,so ming government engaged in positively and showed concern for theirs out of the ordinary unusual,forming perfect and all -round defense works, Under guide of policy of performing garrison duty, the ming government set up those northwest border towns,establishing defense works,northwest national defense put in shape,which rely on the Great Wall and work in concert with inside .Borer towns were put up alone the line, there were seven sentry posts outside of the Jiayuguan pass all that northwest national defense works formed and combined points lines and surfaces, guaranteeing the northwest frontier stable and the Ming dynasty safe,however, there were errors in the courses of establishing defense works,so we should learn lessons from the errors .In the light of theirs historic role and value for today ,I begin with my research on the basis of others,research achievements, local chronicles, maps of territory and census registers , taking advantage of historical materials and writings in ming dynasty,probing into the reasons that northwest national defense system were established, cirmstances of set -up and function in northwest.