The oldest Unit of The Armies of Ancient Rome, The Triarii were first created during the early Republic Era (500 BC - 100 BC). They were formed to serve during The Semnite Wars. They were composed of only the wealthiest of Roman Citizens. As such, they could well afford the very best Armor and weapons. They were used as "3rd Rank" Soldiers and were considered "Heavy Infantry". The Triarii used the "Phalanx" or "Spear Square" Tactic to break up Enemy Positions, after they had been exploited by Light Infantry and possibly Cavalry Units. The Triarii were present throughout most of Rome's Military History until The Marian Reforms of 107 BC. No longer only reserved for the wealthy, The Triarii began to include more Common Soldiers. However, their status as Heavy Infantry remained more or less unchanged. Eventually, even this too changed. The cost of maintaining expensive Heavy Armor and weapons became too cost prohibitive for the late Imperial Period. The Triarii were reclassified as Light Infantry.