Sieges were the neutron bombs of ancient warfare—a total concentration of military force on a fixed defensive, usually civilian, position. Whenever a city retreated behind its walls and a standoff loomed, the attacking army surrounded it and cut off its supplies. Capitulation often took months or even years, depending on how well provisioned the town was. The besieging army needed a method to hasten surrender, a way to bring the walls down and allow them to move in for the kill. The Assyrians, one of the oldest-known civilizations (2000-612 b.c.), are thought to have invented siege warfare. One of their most effective weapons was the battering ram, a tool that was used and improved by both the Greeks and the Romans. The first rams were rather crude, consisting of little more than a tree trunk about 15 feet (4.5 m) long hung by a rope...