Triarii Triarii ( Singular : " Triarius " ) were one of the elements of the early Roman military Manipular legions of the early Roman Republic ( 509 BC – 107 BC ) . They were the oldest and among the wealthiest men in the army , and could afford good quality equipment . They wore heavy metal armour and carried large shields , their usual position being the third battle line . During the Camillan era , they fought in a shallow phalanx formation , supported by light troops . In most battles " triarii " were not used because the lighter troops usually defeated the enemy before the " triarii " were committed to the battle . They were meant to be used as a decisive force in the battle , thus prompting an old Roman saying : ' Going to the triarii ' ( " res ad triarios venit " ) , which meant carrying on to the bitter end . History and deployment . " Triarii " may have evolved from the old first class of the army under the Etruscan kings . The first class comprised the richest soldiers in the legion who were equipped with spears , breastplates and large shields , like heavy Greek hoplites . They served as heavy infantry in the early Roman army , and were used at the front of a very large phalanx formation . After a time , engagements with the Samnites and Gauls appear to have taught the Romans the importance of flexibility and the inadequacy of the phalanx on the rough , hilly ground of central Italy . Camillan era . By the 4th century BC , the military formations the Romans had inherited from the Etruscans were still in use . Though their efficiency was doubtful , they proved effective against Rome ' s largely local adversaries . When Gauls invaded Etruria in 390 BC , the inhabitants requested help from Rome . The small contingent Rome sent to repel the Gallic invaders provoked a full - scale attack on Rome . The entire Roman army was destroyed at the Battle of the Allia . This crushing defeat prompted reforms by Marcus Furius Camillus . Under the new system , men were sorted into classes according to wealth , the " triarii " being the richest after the mounted " equites " . " Triarii " were armed with spears , or " hastae " , about 2 metres ( 6½ feet ) long . They also carried sword s , or " gladii " , about 84 centimetres ( 29 inches ) long , in case the spear broke or the enemy drew too close . They fought as hoplites , usually carrying " clipei " , large round Greek shields , and bronze helmet s , often with a number of feathers fixed onto the top to increase stature . Heavy plate armour was favoured , with mail also being popular . Many would paint or engrave portraits of ancestors onto their shield , believing that it would bring them luck in battle . In this type of new Roman legion , the 900 " triarii " formed 15 maniple s , military units of 60 men each , which were in turn part of 15 " ordines " , larger units made up of a maniple of " triarii " , a maniple of " rorarii " and a maniple of " accensi " . The " triarii " stood in the third line of the legion , behind the front line of " hastati " and the second line of " principes " , and in front of the " rorarii " and " accensi " . In a pitched battle , the " leves " , javelin - armed skirmishers who were attached to maniples of " hastati " , would form up at the front of the legion and harass the enemy with javelin fire and cover the advance of the " hastati " , spear armed infantry . If the " hastati " failed to break the enemy , they would fall back and let the " principes " , heavier and more experienced infantry , take over . If the " principes " did not break them , they would retire behind the " triarii " , who would then engage the enemy in turn — hence the expression " rem ad Triarios redisse " , " it has come to the " triarii " " — signalling an act of desperation . The " equites " , cavalrymen , were used as flankers and to pursue routing enemies . The " rorarii " , the poorer reserve soldiers , and " accensi " , the least dependable troops armed with sling s , would be used in a support role , providing mass and supporting wavering areas of the line . Polybian system . By the time of the second Punic war of the late 3rd century BC , this system proved inefficient against enemies such as Carthage . After a series of more " organic " changes as opposed to a single intentional reform , a new system gradually came into being . Infantry were sorted into classes according to age and experience rather than wealth , the " triarii " being the most experienced . Their equipment and role was very similar to the previous system , except they now carried " scuta " , large rectangular shields that offered a greater degree of protection than the old round " clipeus " . The number of " triarii " had been reduced to 600 per legion , now forming 10 maniples of 60 men each . The " triarii " still made up the third line in the legion , behind the front line of " hastati " and the second line of " principes " , but the " rorarii " and " accensi " had been phased out . " Leves " had been replaced with " velites " , who had a similar role but were also attached to " principes " and " triarii " . Pitched battles were conducted in a similar fashion : the " velites " would gather at the front and fling javelins to cover the advance of the " hastati " . If the " hastati " failed to break the enemy , they would fall back on the " principes " , who now carried swords rather than spears . If the " principes " could not break them they would retire behind the " triarii " , who would then engage the enemy . This order of battle was almost always followed , the battle of the Great Plains and the battle of Zama being among the few notable exceptions . At the Great Plains , Scipio , the Roman general , formed his men up in the usual manner , but once the " hastati " had begun to engage the enemy , he used his " principes " and " triarii " as a flanking force , routing the opposing Carthaginians . At Zama , Scipio arranged his men into columns , side by side , with large lanes in between . The opposing Carthaginian elephants were drawn into these lanes where many were killed by " velites " without inflicting many casualties on the Romans . Once the surviving elephants had been routed , he formed his men into a long line with his " triarii " and " principes " in the centre and " hastati " on the flanks , ready to engage the Carthaginian infantry . Marian reforms . With the formal military reforms of Gaius Marius in 107 BC , implemented to combat a shortage of manpower due to wars against Jugurtha in Africa and Germanic tribes to the north , the different classes of units were scrapped entirely . The wealth and age requirements were removed ; anyone could join as a career , rather than as service to the city , and all would be equipped as " milites " , with the same , state - purchased equipment . Auxiliaries , local irregular troops , would fulfill other roles , serving as archers , skirmishers and cavalry . Sallust , in his " Jugurthine War " , describes several instances in which Roman or allied regular heavy infantry were equipped with light equipment and used as light footsoldiers . This was supposedly a common practice .