Why did ancient soldiers wear battle shirts? What's the role?

In ancient times, people used cold weapons to fight, shooting with arrows from a distance, cutting with knives at close range and poking with spears. ...

In ancient times, there were many metal pieces sewn on the cloth base, which could prevent the stab injury of arrows, knives and spears, reduce the degree of injury or even completely avoid it. According to the density and thickness of metal sheets, shirts can be divided into light and heavy armor.

In addition to the battle robes, soldiers also have metal helmets on their heads to protect their heads from attacks.