I was doing a little reading last night on how the Roman legion fought in the later Republican era, before the so-called “Marian” reforms.
The Roman infantry fought in three lines.
Originally, the arms and equipment they used were derived from earlier times when the wealth of an individual determined their equipment and thus their role on the field of battle. By the period I am interested in this was changing due to the manpower demands brought on by the Punic wars. Filling out the ranks meant drafting in men from the poorer classes who would not normally be able to equip themselves. This meant the State had to step in with arms, armour and clothing.
Without going into the administrative structure of the legion, it seems to me that there were three types of infantry in the legion, as well as a small body of cavalry. These infantry types were the velites (light infantry skirmishers), the hastatii and principes (who by this time might as well be collapsed together into the designation “medium” infantry) and the triarii (or for all intents and purposes, “heavy” infantry).
Taking the velites first, you had a body of lightly armed and equipped men whose role was to contest the enemy advance, cause disruption among his ranks and hopefully counter his own skirmishers.
Their role pretty much ended as soon as the battle lines engaged.
The fairly interchangeably equipped principes and hastatii were equipped with a mail shirt, a helmet and a greave for their leading leg. They bore an “Italian” shield (or scutum) a javelin (or pilum) and a short, stabbing sword. Drawn up in two lines, one behind the other, they formed the main part of the battle line.
Their role was to close with the enemy, discharge their missiles from close range and then follow up with sword and shield.
Should the effort of this first line be in van, the first line would fall back through gaps in the second who would renew the assault.
In the meantime, the men of the first line would collect their second pilae and themselves stand ready to rejoin the effort should the second line prove unsuccessful.
One assumes that each line could theoretically assault twice before running out of pilae!
The triarii formed the third line in the battle-array. Armed as they were with a spear and shield (and much the same panoply as the medium infantry) they formed a phalanx which could I assume cover a retreat or act as a refuge for broken troops.
Good brief description here.