Usksider has asked me When did we discover effective armour against bolts and arrows? The simple bow in ancient Egypt could kill at 50-100 yards but it would not penetrate leather armour at these ranges. During the New Kingdom (c.1500BC) the reed arrow was developed and bronze tips used at short range with the composite bow could easily pierce leather armour.
Because of this, the Egyptians also recognized the need to develop a thicker type of body armour and one was made from leather and metal. Against armoured soldiers the ancient archers probably became proficient at aiming for the back of the neck, top of the central soldiers and lower lumbar region of the spine, the areas most exposed on the back of a running man.
Legionaires from the 1st century AD onwards wore various types of armour. Below I have listed 3 types of armour and briefly mentioned the various effects caused by arrows.
1) ring mail (lorica hamata) - easy to penetrate, the arrow would be locked into place by the damaged mail rings making the arrow difficult to extract or the arrow would break upon impact. (The latter can be seen in the case of Eurypylos and Aeneas.)
2) scale armour (lorica squamata) - fairly easy to penetrate
3) strip plate armour (lorica segmentata) - none of the arrowheads penetrated to a depth sufficient to cause a fatal wound even at a range of seven meters. (Yet a hail of missiles could make a serious dent in the morale of soldiers.)
From around c.1250 plate armour was introduced to reinforce chain mail reflecting the recognised need to respond to the development of the long bow, which dominated warfare for centuries to come.
