This article is part of the series on: Military of ancient Rome (portal) 753 BC – AD 476
Structural history
Roman army (unit types and ranks, legions, auxiliaries, generals)
Roman navy (fleets, admirals)
Campaign history
Lists of wars and battles
Decorations and punishments
Technological history
Military engineering (castra, siege engines, arches, roads)
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The Latin word castra,^[1] with its singular castrum, was used by the ancient Romans to mean buildings or plots of land reserved to or constructed for use as a military defensive position. The word appears in both Oscan and Umbrian (dialects of Italic) as well as in Latin.^[2] It may have descended from Indo-European to Italic. In classical Latin the word castra always means "great legionary encampment", both "marching", "temporary" ones and the "fortified permanent" ones, while the diminutive form castellum was used for the smaller forts, which were usually, but not always, occupied by the auxiliary units and used as logistic bases for the legions, as explained by Vegetius.^[3] A generic term is praesidium ("guard post or garrison"). The terms stratopedon ("army camp") and phrourion ("fort") were used by Greek language authors, in order to designate the Roman castra and the Roman castellum respectively. In English, the terms "Roman fortress", "Roman fort" and "Roman camp" are commonly used for the castra. However the scholars' convention always requires the use of the word "camp", "marching camp" and "fortress" as a translation of castra and the use of the word "fort" as a translation of castellum and this type of convention is usually followed and found in all the scholarly works.^[4]

Etymology[link]

According to Julius Pokorny, Indogermanisches Etymologisches Woerterbuch, page 586 under kes- (palatal k), Oscan castrous (genitive case) and Umbrian castruo, kastruvuf (nominative case) have the same original meaning as castrum, which was an estate, or a tract of land. Being the term used to designate a private estate, in Latin the word castrum was probably then the term for an estate or a tract of land enclosed by a fence or a wooden or stone wall of some kind, as seems to be used in a few passages in Cornelius Nepos' works.^[5]

The American Heritage Dictionary, following Julius Pokorny, lists *kes-, "cut", as the root. One castrum was a reservation of land "cut off" for military use. It could be an entire base, such as castrum Moguntiacum, or it could be a single fortified building. From the latter use came the English word castle (castellum, a diminutive of castrum).

In Latin the term Castrum is much more frequently used as proper name of geographical locations: e.g. Castrum Album, Castrum Inui, Castrum Novum, Castrum Truentinum, Castrum Vergium.

Castra in the plural refers to a collection of structures. Considering that the earliest structures were tents, which were cut out of hide or cloth, one castrum may well be a tent, with the plural meaning tents.^[6] All but the most permanent bases housed the men in barracks of tents placed in quadrangles and separated by numbered streets. The term castra then means Marching Camp, Temporary Camp, Permanent Camp, Fortified Camp and Fortress, always designating a great legionary encampment.

The Plural was also used as Geographical place proper name, as Castra Cornelia, and from the plural come the English place-name suffixes such as -caster and -chester; e.g., Winchester, Lancaster.

The commonest Latin syntagmata for the term castra are:

• castra stativa: permanent camp/fortress
• castra aestiva: summer camp/fortress
• castra hiberna: winter camp/fortress
• castra navalia or castra nautica: navy camp/fortress

Castrorum Filius was one of names used by the emperor Caligula and then also by other emperors.

"Castro", also derived from "Castrum", is a common Spanish family name, as well as a name-place in Spain and Spanish-speaking countries, Italy and the Balkan, either by itself or in various compounds such as Argyrocastro (see Castro).

Types of castra[link]

Basic ideal plan of a Roman castrum. (1) Principia; (2) Via Praetoria; (3) Via Principalis; (4) Porta Principalis Dextra; (5) Porta Praetoria (main gate); (6) Porta Principalis Sinistra; (7)Porta Decumana (back gate).

The best known type of castra is the camp, a military town designed to house and protect the soldiers and their equipment and supplies when they were not fighting or marching. Regulations required a major unit in the field to retire to a properly constructed camp every day. "...as soon as they have marched into an enemy's land, they do not begin to fight till they have walled their camp about; nor is the fence they raise rashly made, or uneven; nor do they all abide ill it, nor do those that are in it take their places at random; but if it happens that the ground is uneven, it is first leveled: their camp is also four-square by measure, and carpenters are ready, in great numbers, with their tools, to erect their buildings for them."^[7] To this end a marching column ported the equipment needed to build and stock the camp in a baggage train of wagons and on the backs of the soldiers.

Camps were the responsibility of engineering units to which specialists of many types belonged, officered by architecti, "chief engineers", who requisitioned manual labor from the soldiers at large as required. They could throw up a camp under enemy attack in as little as a few hours. Judging from the names, they probably used a repertory of camp plans, selecting the one appropriate to the length of time a legion would spend in it: tertia castra, quarta castra, etc., "a camp of three days", "four days", etc.^[8]

More permanent camps were castra stativa, "standing camps". The least permanent of these were castra aestiva or aestivalia, "summer camps", in which the soldiers were housed sub pellibus or sub tentoriis, "under tents".^[9] Summer was the campaign season. For the winter the soldiers retired to castra hiberna containing barracks and other buildings of more solid materials, with timber construction gradually being replaced by stone.^[10]

The camp allowed the Romans to keep a rested and supplied army in the field. Neither the Celtic nor Germanic armies had this capability: they found it necessary to disperse after only a few days; meanwhile, their open camps invited attack when they were least prepared.

Plan of the fort[link]

Reconstructed gateway of a Castra Stativa. Note the battlements, the Roman arches, the turres.

Reconstruction of the specula or vigilarium (Germanic burgus), "watchtower", a type of castrum, of Fectio. An ancient watchtower would have been surrounded by wall and ditch.^[11]

Sources and origins[link]

Even from the most ancient times Roman camps were constructed according to a certain ideal pattern, formally described in two main sources, the De Metatione Castrorum or De Munitionibus Castrorum by either Hyginus Gromaticus or Pseudo-Hyginus and the works of Polybius.^[12] Vegetius has a small section on entrenched camps as well. The terminology varies some but the basic plan is the same.^[13] To readers of the Rig Veda the pattern is strikingly familiar, as it is essentially the same as that described as being used by the Aryans invading Iron Age India to lay out a village^{[citation needed]}.^{[dubious – discuss]} That is not to say non-Indo-European peoples did not use it either. The hypothesis of an Etruscan origin is a viable alternative.^[14]

Layout[link]

The reconstructed porta praetoria of the castle Pfünz, Germany, near the Raetian Limes.

The ideal enforced a linear plan for a camp or fort: a square for camps to contain one legion or smaller unit, a rectangle for two legions, each legion being placed back-to-back with headquarters next to each other. Laying it out was a geometric exercise conducted by experienced officers called metatores, who used graduated measuring rods called decempedae ("10-footers") and gromatici who used a groma, a sighting device consisting of a vertical staff with horizontal cross pieces and vertical plumb-lines. Ideally the process started in the centre of the planned camp at the site of the headquarters tent or building (principia). Streets and other features were marked with coloured pennants or rods.

Wall and ditch[link]

Castra at Masada. Note the classical "playing-card" layout.

The Castra's special structure also defended from attacks.

The base (munimentum, "fortification") was placed entirely within the vallum ("wall"), which could be constructed under the protection of the legion in battle formation if necessary. The vallum was quadrangular aligned on the cardinal points of the compass. The construction crews dug a trench (fossa), throwing the excavated material inward, to be formed into the rampart (agger). On top of this a palisade of stakes (sudes or valli) was erected. The soldiers had to carry these stakes on the march.^[15] Over the course of time, the palisade might be replaced by a fine brick or stone wall, and the ditch serve also as a moat. A legion-sized camp always placed towers at intervals along the wall with positions between for the division artillery.

Interval[link]

Around the inside periphery of the vallum was a clear space, the intervallum, which served to catch enemy missiles, as an access route to the vallum and as a storage space for cattle (capita) and booty (praeda). Legionaries were quartered in a peripheral zone inside the intervallum, which they could rapidly cross to take up position on the vallum. Inside of the legionary quarters was a peripheral road, the Via Sagularis, probably "service road", as the sagum, a kind of cloak, was the garment of slaves.

Streets, gates and central plaza[link]

Reconstructed east gate of a Castra Stativa, a more permanent base.

Every camp included "main street", which ran unimpeded through the camp in a north-south direction and was very wide. The names of streets in many cities formerly occupied by the Romans suggest that the street was called cardo or Cardus Maximus. This name applies more to cities than it does to ancient camps.^[16]

Typically "main street" was the via principalis. The central portion was used as a parade ground and headquarters area. The "headquarters" building was called the praetorium because it housed the praetor or base commander ("first officer"), and his staff. In the camp of a full legion he held the rank of consul or proconsul but officers of lesser ranks might command.

On one side of the praetorium was the quaestorium, the building of the supply officer, or quaestor ("seeker"). On the other side was the forum, a small duplicate of an urban forum, where public business could be conducted. Along the Via Principalis were the homes or tents of the several tribunes in front of the barracks of the units they commanded.

The Via Principalis went through the vallum in the Porta Principalis Dextra ("right principal gate") and Porta Principalis Sinistra ("left, etc."), which were gates fortified with turres ("towers"). Which was on the north and which on the south depends on whether the praetorium faced east or west, which remains unknown.

The central region of the Via Principalis with the buildings for the command staff was called the Principia (plural of principium). It was actually a square, as across this at right angles to the Via Principalis was the Via Praetoria, so called because the praetorium interrupted it. The Via Principalis and the Via Praetoria offered another division of the camp into four quarters.

Porta Praetoria at Porolissum, Dacia (modern Romania)

Across the central plaza (principia) to the east or west was the main gate, the Porta Praetoria. Marching through it and down "headquarters street" a unit ended up in formation in front of the headquarters. The standards of the legion were located on display there, very much like the flag of modern camps.

On the other side of the praetorium the Via Praetoria continued to the wall, where it went through the Porta Decumana. In theory this was the back gate. Supplies were supposed to come in through it and so it was also called, descriptively, the Porta Quaestoria. The term Decumena, "of the 10th", came from the arranging of manipuli or turmae from the first to the 10th, such that the 10th was near the intervallum on that side. The Via Praetoria on that side might take the name Via Decumena or the entire Via Praetoria be replaced with Decumanus Maximus.^[17]

Canteen[link]

In peaceful times the camp set up a marketplace with the natives in the area. They were allowed into the camp as far as the units numbered 5 (half-way to the praetorium). There another street crossed the camp at right angles to the Via Decumana, called the Via Quintana, "5th street". If the camp needed more gates, one or two of the Porta Quintana were built, presumably named dextra and sinistra. If the gates were not built, the Porta Decumana also became the Porta Quintana. At "5th street" a public market was allowed.^{[citation needed]}

Major buildings[link]

Not much remains of these horrea (granaries) at Arbeia, but the longitudinal supports for the floor can be seen.

The Via Quintana and the Via Principalis divided the camp into three districts: the Latera Praetorii, the Praetentura and the Retentura. In the latera ("sides") were the Arae (sacrificial altars), the Auguratorium (for auspices), the Tribunal, where courts martial and arbitrations were conducted (it had a raised platform), the guardhouse, the quarters of various kinds of staff and the storehouses for grain (horreae) or meat (carnarea). Sometimes the horreae were located near the barracks and the meat was stored on the hoof. Analysis of sewage from latrines indicates the legionary diet was mainly grain. Also located in the Latera was the Armamentarium, a long shed containing any heavy weapons and artillery not on the wall.

Roman artillery piece (Onager)

The Praetentura ("stretching to the front") contained the Scamnum Legatorum, the quarters of officers who were below general but higher than company commanders (Legati).^[18] Near the Principia were the Valetudinarium (hospital), Veterinarium (for horses), Fabrica ("workshop", metals and wood), and further to the front the quarters of special forces. These included Classici ("marines", as most European camps were on rivers and contained a river naval command), Equites ("cavalry"), Exploratores ("scouts"), and Vexillarii (carriers of vexillae, the official pennants of the legion and its units). Troops who did not fit elsewhere also were there.

The part of the Retentura ("stretching to the rear") closest to the Principia contained the Quaestorium. By the late empire it had developed also into a safekeep for plunder and a prison for hostages and high-ranking enemy captives. Near the Quaestorium were the quarters of the headquarters guard (Statores), who amounted to two centuries (companies). If the Imperator was present they served as his bodyguard.

Barracks[link]

A sanitary channel at Potaissa, Dacia (modern Romania). It is placed cross-slope with a slight decline and then exits down-slope.

Further from the Qaestorium were the tents of the Nationes ("natives"), who were auxiliaries of foreign troops, and the legionaries themselves in double rows of tents or barracks (Strigae). One Striga was as long as required and 18 m wide. In it were two Hemistrigia of facing tents centered in its 9 m strip. Arms could be stacked before the tents and baggage carts kept there as well. Space on the other side of the tent was for passage.

In the northern places like Britain were it got cold in the winter they would make wood or stone barracks.The Romans would also put a fire place in the barracks. They had about 3 bunk beds in it. They had a small room beside it where they put their armour, it was as big as the tents. They would also make these barracks if the fort they had was going to stay there for good. ^[19]