The wall originated in the Warring States period. With the fall of the Zhou king, [G 17 / principalities] grabbed pieces of China and built walls to protect themselves. These were simple structures - a horizontal wall and beacon tower. Watch-men in castles or fortresses would watch the beacon for sign of impending attacks. Gradually, these walls were linked up. Even earlier walls are thought to have existed; mention is made of walls as early as the ninth century BC when the Zhou king was supposed to have built a small wall against attacks by the Xiangyun tribe.
