In ancient battle unity existed, Colonel Ardant Du Picq says, at least with the Greeks and the Romans:
The soldier was known to his officer and comrades; they saw that he fought.
In modern armies where losses are as great for the victor as for the vanquished, the soldier must more often be replaced. In ancient battle the victor had no losses. To-day the soldier is often unknown to his comrades. He is lost in the smoke, the dispersion, the confusion of battle. He seems to fight alone. Unity is no longer insured by mutual surveillance. A man falls, and disappears. Who knows whether it was a bullet or the fear of advancing further that struck him! The ancient combatant was never struck by an invisible weapon and could not fall in this way. The more difficult surveillance, the more necessary becomes the individuality of companies, sections, squads. Not the least of their boasts should be their ability to stand a roll call at all times.