century, the significance of the classical siege declined. With the advent of mobile warfare, a single fortified stronghold is no longer as decisive as it once was. While traditional sieges do still occur, they are not as common as they once were due to changes in modes of battle, principally the ease by which huge volumes of destructive power can be directed onto a static target. Modern sieges are more commonly the result of smaller hostage, militant, or extreme resisting arrest situations. Ancient period The necessity of city walls The Assyrians deployed large labour forces to build new palaces, temples, and defensive walls. Some settlements in the Indus Valley civilization were also fortified. By about 3500 BC, hundreds of small farming villages dotted the Indus River floodplain. Many of these settlements had fortifications and planned streets. The stone and mud brick houses of Kot Diji were clustered behind massive stone flood dikes and defensive walls, for neighbouring communities quarrelled constantly about the control of prime agricultural land. Mundigak (c. 2500 BC) in present-day south-east Afghanistan has defensive walls and square bastions of sun-dried bricks. City walls and fortifications were essential for the defence of the first cities in the ancient Near East. The walls were built of mudbricks, stone, wood, or a combination of these materials, depending on local availability. They may also have served the dual purpose of showing potential enemies the might of the kingdom. The great walls surrounding the Sumerian city of Uruk gained a widespread reputation. The walls were in length, and up to in height. Later, the walls of Babylon, reinforced by towers, moats, and ditches, gained a similar reputation. In Anatolia, the Hittites built massive stone walls around their cities atop hillsides, taking advantage of the terrain. In Shang Dynasty China, at the site of Ao, large walls were erected in the 15th century BC that had dimensions of in width at the base and enclosed an area of some squared. The ancient Chinese capital for the State of Zhao, Handan, founded in 386 BC, also had walls that were wide at the base; they were tall, with two separate sides of its rectangular enclosure at a length of 1,530 yd (1,400 m). The cities of the Indus Valley Civilization showed less effort in constructing defences, as did the Minoan civilization on Crete. These civilizations probably relied more on the defence of their outer