The Romans originally used the phalanx; and the lines were formed according to the classes determined by the centuries.

Those who were sufficiently wealthy to purchase a full suit of armour, formed the front ranks; those who could only purchase a portion of the defensive weapons, filled the centre; and the rear was formed by the poorer classes, who scarcely required any armour, being protected by the lines in front.

From this explanation, it is easy to see why, in the constitution of the centuries by Servius Tullius, the first class were perfectly covered with mail, the second had helmets and breast-plates but no protection for the body, the third, neither a coat of mail, nor greaves.6.The defects of this system are sufficiently obvious; an unexpected attack on the flanks, the breaking of the line by rugged and uneven ground, and a thousand similar accidents exposed the unprotected portions of the army to destruction besides, a line with files ten deep was necessarily slow in its movements and evolutions.
Another and not less important defect was, that the whole should act together; and consequently, there were few opportunities for the display of individual bravery.
7.

It is not certainly known who was the great commander that substituted the living body of the Roman legion for this inanimate mass; but there is some reason to believe that this wondrous improvement was effected by Camil'lus.

Every legion was in itself an army, combining the advantages of every variety of weapon, with the absolute perfection of a military division.
8.