also in defense of cities, where they were placed on the city walls to incinerate any attacking soldiers. Rockets During the Ming dynasty, the design of rockets were further refined and multi-stage rockets and large batteries of rockets were produced. Multi-stage rockets were introduced for naval combat. Like other technology, knowledge of rockets were transmitted to the Middle East and the West through the Mongols, where they were described by Arabs as "Chinese arrows". Infantry In the 2nd century BC, the Han began to produce steel from cast iron. New steel weapons were manufactured that gave Chinese infantry an edge in close-range fighting, though swords and blades were also used. The Chinese infantry were given extremely heavy armor in order to withstand cavalry charges, some 29.8 kg of armor during the Song dynasty. Cavalry The cavalry was equipped with heavy armor in order to crush a line of infantry, though light cavalry was used for reconnaissance. However, Chinese armies lacked horses and their cavalry were often inferior to their horse archer opponents. Therefore, in most of these campaigns, the cavalry had to rely on the infantry to provide support. Between the Jin and Tang dynasty, fully armored cataphracts were introduced in combat. An important innovation was the invention of the stirrup. From early Indian invention, which allowed cavalrymen to be much more effective in combat; this innovation later spread to East, north and west via the nomadic populations of central Asia and to the west by the Avars. However, some believe northern nomads were responsible for this innovation. Some authors, such as Lynn White, claim the use of the stirrup in Europe stimulated development of the medieval knights which characterized feudal Europe. However, this thesis was disputed in the Great Stirrup Controversy by historians such as Bernard Bachrach, although it has been pointed out that the Carolingian riders may have been the most expert cavalry of all at its use. Chemical weapons During the Han dynasty, state manufacturers were producing stink bombs and tear gas bombs that were used effectively to suppress a revolt in 178 AD. Poisonous materials were also employed in rockets and crossbow ammunition to increase their effectiveness. Logistics The Chinese armies also benefited from a logistics system that could supply hundreds of thousands of men at a time. An important innovation by the Chinese was the introduction of an efficient horse harness in the 4th century