text: triarii triarii ( singular : ) 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 high quality equipment . they wore heavy metal armor and carried large shields , their usual position being the third battle line . they were equipped with spears . 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 : ' it comes down to the triarii ' ( res ad ) , 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 ( 6 ½ feet ) long . they also carried swords , 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 , large round greek shields , and bronze helmets , 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 maniples , 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 , " it has come to the triarii " — signaling 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 slings , 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 . 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 , 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 . this was supposedly a common practice .