Gansu is one of the provinces to have most Great Wall sections. The investigation shows that at least five states or dynasties have built Great Wall in Gansu Province. They are the King of Zhao in Qin State (324BC-251BC), Qin Dynasty (221BC-206BC), Han Dynasty (206BC-220), Northern Liang State (401-439) and Ming Dynasty (1368-1644). The overall length has surpassed 4,000 km (2,485 miles). But due to the natural and human factors, many sections have been badly damaged.