The flank companies are intended for light infantry.
In all properly organized armies the infantry constitutes from three-fourths to four-fifths of the entire active force in the field, and from two-thirds to three-fourths, say about seven-tenths of the entire military establishment.

In time of peace this proportion may be slightly diminished.
_Cavalry._--The use of cavalry is probably nearly as old as war itself.
The Egyptians had cavalry before the time of Moses, and the Israelites often encountered cavalry in their wars with their neighbors, though they made no use of this arm themselves until the time of Solomon.
The Greeks borrowed their cavalry from the Asiatics, and especially from the Persians, who, according to Xenophon, held this arm in great consideration.

After the battle of Platea, it was agreed by assembled Greece that each power should furnish one horseman to every ten foot-soldiers.

In Sparta the poorest were selected for this arm, and the cavalry marched to combat without any previous training.

At Athens the cavalry service was more popular, and they formed a well-organized corps of twelve hundred horsemen.