section_path: Reign as Emperor of Qin/Public works/Great Wall
section_name: Great Wall
paragraph_text: Great Wall
  
  Numerous state walls had been built during the previous four centuries, many of them closing gaps between river defences and impassable cliffs. To impose centralized rule and prevent the resurgence of feudal lords, the Emperor ordered the destruction of walls between the former states, which were now internal walls dividing the empire.
  
  However, to defend against the northern Xiongnu nomads, who had beaten back repeated campaigns against them, he ordered new walls to connect the fortifications along the empire's northern frontier. Hundreds of thousands of workers were mobilized, and an unknown number died, to build this precursor to the current Great Wall of China. Transporting building materials was difficult, so builders always tried to use local materials: rock over mountain ranges, rammed earth over the plains. "Build and move on" was a guiding principle, implying that the Wall was not a permanently fixed border. There are no surviving records specifying the length and course of the Qin walls, which have largely eroded away over the centuries.