Titus Livius (Livy), The History of Rome, Book 8
Rev. Canon Roberts, Ed.

8. The terrible severity of the punishment, however, made the soldiers more obedient to their general, and not only did it lead to greater attention being paid to the pickets and sentry duties and the ordering of the outposts, but when they went [2??] into battle for the final contest, this severity proved to be of the greatest service. [3] The battle was exactly like one fought in a civil war; there was nothing in the Latin army different from the Roman except their courage.

At¹ first the Romans used the large round shield called the clipeus, afterwards, when the soldiers received pay, the smaller oblong shield called the scutum was adopted. [4] The phalanx formation, similar to the Macedonian of the earlier days, was abandoned in favour of the distribution into companies (manipuli); the rear portion being broken up into smaller divisions. [5] The foremost line consisted of the hastati, formed into fifteen companies, drawn up at a short distance from each other. [6] These were called the lightarmed companies, as whilst one-third carried a long spear (hasta and short iron javelins, the remainder carried shields. This front line consisted of youths in the first bloom of manhood just old enough for service. [7] Behind them were stationed an equal number of companies, called principes, made up of men in the full vigour of life, all carrying shields and furnished with superior weapons. This body of thirty companies were called the antepilani. [8] Behind them were the standards under which were stationed fifteen companies, which were divided into three sections called vexillae, the first section in each was called the pilus, and they consisted of 180 men to every standard (vexillum). The first vexillum was followed by the triarii, veterans of proved courage; the second by the rorarii, or ‘skirmishers,’ younger men and less distinguished; the third by the accensi, who were least to be depended upon, and were therefore placed in the rearmost line.

[9] When the battle formation of the army was completed, the hastati were the first to engage. If they failed to repulse the enemy, they slowly retired through the intervals between the companies of the principes who then took up the fight, the hastati following in their rear. [10] The triarii, meantime, were resting on one knee under their standards, their shields over their shoulders and their spears planted on the ground with the points upwards, giving them the appearance of a bristling palisade. [11] If the principes were also unsuccessful, they slowly retired to the triarii, which has given rise to the proverbial saying, when people are in great difficulty ‘matters have come down to the triarii.’ [12] When the triarii had admitted the hastati and principes through the intervals separating their companies, they rose from their kneeling posture [13??] and instantly closing their companies up they blocked all passage through them and in one compact mass fell on the enemy as the last hope of the army. [14] The enemy who had followed up the others as though they had defeated them, saw with dread a now and larger army rising apparently out of the earth.

There were generally four legions enrolled, consisting each of 5000 men, and 300 cavalry were assigned to each legion. [15] A force of equal size used to be supplied by the Latins, now, however, they were hostile to Rome.

The two armies were drawn up in the same formation, and they knew that if the maniples kept their order they would have to [16??] fight, not only vexilla with vexilla, hastati with hastati, principes with principes, but even centurion with Centurion.

[17] There were amongst the triarii two centurions, one in each army —the Roman, possessing but little bodily strength but an energetic and experienced soldier, the Latin, a man of enormous strength and a splendid fighter —very well known to each other because they had always served in the same Company. [18] The Roman, distrusting his own strength, had obtained the consuls' permission before leaving Rome to choose his own sub-centurion to protect him from the man who was destined to be his enemy. [19] This youth, finding himself face to face with the Latin centurion, gained a victory over him.