Zhou army. The fourth King, Zhao of Zhou (975-957 BC) suffered a severe defeat at the battle against the State of Chu on the Han River, where the entire Six Armies of the West were lost and had to be rebuilt. This led to the end of Zhou dominance as opponents began emboldened and challenged its strength frequently. In the Spring and Autumn period, archery switched from targeted shooting to massed volleys. By the end of the Spring and Autumn Period cavalry had appeared on the battlefield, and the chariot would gradually revert to being a command platform in the course of the ensuing Warring States period. Warring States By the time of the Warring States, reforms began that abolished feudalism and created powerful, centralized states. The power of the aristocracy was curbed and for the first time, professional generals were appointed on merit, rather than birth. Technological advances such as iron weapons and crossbows put the chariot-riding nobility out of business and favored large, professional standing armies, who were well-supplied and could fight a sustained campaign. The size of armies increased; whereas before 500 BC Chinese field armies numbered in the tens of thousands, by 300 BC armies regularly included up to a couple of hundred thousand drafted soldiers, accompanied by cavalry. For example, during the Battle of Changping the state of Qin drafted all males over 15 years of age. Although these conscripts with one to two years of training would be no match individually against aristocratic warriors with years of experience, they made up for it with superior standardization, discipline, organization, and size. Although most soldiers were conscripts, it was also common to select soldiers based on specific qualifications. The Confucian adviser Xun Zi claimed that foot soldiers from the Wei state were required to wear armor and helmets, shoulder a crossbow with fifty arrows, strap a spear and sword, carry three days' supply of rations, and all the while march 50 kilometers in a day. When a man meets this requirement, his household would be exempted from all corvée labor obligations. He would also be given special tax benefits on land and housing. However, this policy made soldiers in the Wei state difficult to replace. In addition, cavalry was introduced. The first recorded use of cavalry took place in the Battle of Maling, in which general Pang Juan of Wei led his division of 5,000 cavalry