The lōrīca segmentāta was a type of segmented armour exclusively used in the Roman Empire, but the Latin name was first used in the 16th century (the ancient form is unknown, although it is possible that the Romans referred to the armour as "lorica laminata"). The armour itself consisted of broad ferrous (originally iron, but steel in modern recreations) strips ('girth hoops') fastened to internal leather straps. The strips were arranged horizontally on the body, overlapping downwards, and they surrounded the torso in two halves, being fastened at the front and back. The upper body and shoulders were protected by additional strips ('shoulder guards') and breast- and backplates. The form of the armour allowed it to be stored very compactly, since it was possible to separate it into four sections. The fitments that closed the various plate sections together (buckles, lobate hinges, hinged straps, tie-hooks, tie-rings, etc.) were, however, made of brass (copper-zinc alloy, with a composition of approximately 75% Cu: 25% Zn).
During the time of its use, it was modified several times, the currently recognised types being the Kalkriese, Corbridge and Newstead types. There was, however, a considerable overlap between these types in use and the Corbridge and Newstead types are often found at the same site (e.g. at Caerleon [Wales], Carnuntum [Austria], Carlisle [England] and Leon [Spain]). It is possible that there was a fourth type, a hybrid of the banded armour together with scale shoulder defences. However, this is only known from a badly damaged statue originating at Alba Julia in Romania. The currently accepted range for the use of the armour is from about 9 B.C. (Dangstetten) to the late 3rd century A.D. (Leon). However, similar armouring techniques were used during the 16th century, employing sliding rivets and this was known as anima. Introduced in the early 1st century CE, the armor saw widespread use during the period of 2nd-3rd centuries CE.
The question (as to precisely who used the armour) is debated. The major problem is that finds of the armour have turned up in very many fort sites that are known to have been garrisoned by only auxiliary troops, i.e. where the legions were not based. If the legions were, indeed, broken up and distributed around all these small bases, then it implies a tactical use of the legions that has not previously been considered. Hitherto, the legions were regarded as shock troops employed only 'en masse' and not broken up into penny packets. M.C. Bishop, however, has argued that we need to examine the way in which the various troop types were armed and deduce from this what their battle roles were, rather than trying to consider who-wore-what. Succintly put, the legions were armed and trained for close-order combat while the auxiliary forces, just as numerous, were more accustomed to open order fighting, although they could be employed as the legions were (e.g. at Mons Graupius) if circumstances demanded this.
The view that auxilia were light troops originates from Vegetius' comment that "auxilia are always joined as light troops with the legions in the line". It is true that some specialist units in the auxilia, such as Syrian archers and Numidian cavalry wore light armour (or none). But they were a small minority of the auxilia. Most auxiliary cohortes contained heavy infantry similar to legionaries. There is a clear difference in armour between the two corps shown on Trajan's Column. This is a monument erected in 113 in Rome to commemorate the conquest of Dacia by Emperor Trajan (ruled 97-117): its bas-reliefs are a key source for Roman military equipment. Auxilia are generally shown wearing chain mail (lorica hamata) cuirasses or simple leather corslets, and carrying oval shields. Legionaries are depicted wearing laminated-strip armour (lorica segmentata) and with curved rectangular shields. But on another Trajanic monument, the Adamclisi Tropaeum, the lorica segmentata does not appear at all, and legionaries and auxilia alike are depicted wearing either chain mail or scales (lorica squamata). Some experts are of the opinion that the Adamclisi monument is a more accurate portrayal of normality, with the segmentata used rarely, maybe only for set-piece battles and parades. This viewpoint considers the figures in Trajan's Column to be highly stereotyped, in order to distinguish clearly between different types of troops. In any event, both corps were equipped with the same weapons: gladius (a close-combat stabbing sword) and javelins, although the type of javelin known as a pilum seems to have been provided to legionaries only. Goldsworthy points out that the equipment of both corps were roughly equal in weight. It should also be noted that Legionaries were required to purchase their own arms and armour (either by supplying it themselves or purchasing it from the military) so that armour could vary considerably from soldier to soldier. One man may have used a Lorica Hamata, while the man on his right the Segmentata. During the 3rd century, when all peregrini were granted citizenship, and therefore legionaries lost their social superiority. The lorica segmentata eventually disappeared from Roman use, most likely due to its high cost and difficult maintenance despite its good qualities, although it appears to have still been in use in early 4th century, being depicted in the Arch of Constantine erected in 315 during the reign of Constantine I to commemorate his military achievements.