Before the warring states of China were united, each state had its own territory and own military for defence. Following the unification of the states, a much more organised army was established. Although the states were united, emperors still wanted to claim more territory and an army was needed to conquer neighbouring peoples and claim their land. For many centuries, China was under threat of attack from Mongol tribes to the north and much of its military was involved with defending Chinese lands.
The army
During the Han dynasty, China was frequently at war. It was also under frequent threat from enemies to the north. China's army was made up mainly of citizens who served in the army for a period of two years at some time in their lives. During times of peace, the army was deployed to conquer peoples and bring more land under Chinese rule.There is no evidence to suggest that ancient Chinese soldiers fought in a particular formation.
Soldiers
During Han times all able men between the ages of 23 and 56 were obliged to serve in the army for a period of two years. This meant that there was always a mobilised fighting force in ancient China. Men were also called to serve in the military in case of an emergency, even if they had previously served their two years. Men who served their time as soldiers during peace time, or when they were not needed on a campaign, were required to perform guard duty, usually at points along the wall or in the cities.
Soldiers had a relatively low status in society. They were not paid for their service but they did receive food and equipment. They were required to wear a full uniform which was also provided.
Weapons
China's early armies fought using chariots and bronze weapons. Later, as weaponry and metalworking developed, soldiers used iron weapons and cavalry. Weapons included bows and arrows and swords. The development of the crossbow in the fourth century BC meant that chariots became redundant. The crossbow had a range of about 200 metres and could pierce armour. It became a very valuable weapon in ancient Chinese warfare.
Armour
Armour was usually made from metal or leather. Small pieces of leather and metal were overlapped and attached to cloth. This provided protection but also allowed the soldiers flexibility of movement. Leather armour was usually lacquered to give extra strength. Dating from Han times, helmets were also worn.
Defence
The army was often engaged in defending China's northern frontier from enemy tribes. Some of these tribes posed a particular threat as many of the soldiers had grown up learning to fight and were competent horseback fighters. This was in contrast to China's army, many of whom had little formal training or experience in battle and who were only exposed to warfare when they were called up to serve their two years.
Ancient Military, 2012.