 Central policy alone did not decide whether the walls would be built, as various "defense commands" (邊鎮, "biānzhèn") along the border possessed considerable autonomy to deal with the nomads, leading to a decentralized approach to wall-building along the frontier.Each wall-building project was designed to meet imminent or potential threats along short sections of the empire's northern border, never larger in scope than a single regional defence command, and were often as short as a few hundred meters.In most cases, frontier policy decisions of this period were made by the supreme commander or the grand coordinator in charge of the defence command, who would then send their proposals to the Ministry of War (兵部, "Bīngbù") and the emperor for approval.