Ab urbe condita
Titus Livius (Livy)
Livy. History of Rome, Volumes 1-2. Roberts, Canon, Rev, translator. London, New York: J. M. Dent and Sons; E. P. Dutton and Co., 1912.
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.
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.