Handan, once well-defended from southern attack by a bend in the Zhang River, was a city of the state of Zhao during the Warring States Period (5th–3rd centuries BCE) of Chinese history. It was their second capital, after Zhongmu. King Wuling of Zhao turned Zhao into one of the Qin state's most stalwart foes, pioneering the use of walls to secure new frontiers (which would inspire the eventual construction of the Great Wall of China). The city was conquered by the State of Qin after the virtual annexation of Zhao by Qin except for the Dai Commandery. The first emperor of China, Qin Shi Huang was born in Handan, the child of a statesman from the state of Qin and after successfully conquering Zhao he ordered all enemies of his mother to be buried alive. The conquest of Zhao, particularly the Qin siege of Handan, is featured extensively in Chen Kaige's classic film, "The Emperor and the Assassin".