Limes (Roman Empire)

Map of fortifications and castles in North Britain around 155 AD (most forts on and south of Hadrian's Wall have been omitted).

This section of limes existed from the 1st to the 5th century AD and ran through the provinces of:

• Britannia Inferior
• Britannia Superior

The limes in Britain (Limes Britannicus) is on the territory of the present-day United Kingdom in England, Scotland and Wales. From the 1st to the 2nd century, the Gask Ridge and the Stanegate, with their chains of Roman camps and watchtowers, marked the northern boundary of Britannia. Later the isthmuses in the north between the Firth of Forth and Firth of Clyde were guarded by the defences of the Antonine Wall and the line between the mouth of the Tyne and Solway Firth by Hadrian's Wall. The perimeter defence of Hadrian's Wall was achieved through the construction of camps (castella) on the lowlands, which were built along the most important roads in the north. Security and monitoring on the coasts in the west and southeast were achieved by camps and by chains of watchtowers or signal towers, both along the coastline and along main roads in the interior.

The occupying forces, Exercitus Britannicus, consisted mostly of cohorts of auxilia. The strategic reserve comprised three legions based in Eburacum (York), Isca Silurum and Deva. The observation and surveillance of the waters around the British Isles was the responsibility of the Classis Britannica, whose headquarters was in Rutupiae (Richborough). Legions auxilia cohorts and the fleet were commanded by the provincial governors. From the 3rd century, units of comitatenses, limitanei and liburnaria (marines) came under the command of two generals:

• Comes Britanniarum
• Dux Britanniarum

Map of British and Gallic forts on the Saxon Shore

This section of the limes existed from the 3rd to 5th centuries AD and covered the provinces of:

• Britannia Inferior
• Belgica
• Lugdunensis
• Aquitania

This limes of the Late Antiquity ran through the territory of the present-day United Kingdom and France. In the 3rd century, a separate military district, the Litus Saxonicum, was established on the British side of the English Channel between the estuaries of the Wash and the Solent, to repel Saxon pirates and plunderers. The Gallic side of the English Channel and Atlantic coast were included therein. Monitoring and coastal surveillance were carried out by a chain of watchtowers or signal towers, camps and fortified ports (Gaul). Most of the Saxon Shore camps probably served as naval bases.

The garrisons of the camps were composed of infantry and several cavalry regiments. Monitoring and surveillance of the Channel were the responsibility of the Classis Britannica and Classis Sambrica, whose headquarters were in Locus Quartensis (Port d'Etaple), guarding the mouth of the River Somme. The units of comitatenses, limitanei and liburnaria in this area came under the command of three generals:

• Comes litoris Saxonici per Britanniam (Count of the Saxon Shore)
• Dux Belgicae secundae
• Dux tractus Armoricani et Nervicani

Map of the legion camps and forts in Germania Inferior

This section of limes existed from the 1st to the 5th century AD and ran through the province of Lower Germania (Germania Inferior).

It lies on the territory of today's Netherlands and Germany. This limes was a river border (limes ripa) on the Rhine, defended by a chain of camps, that ran from the North Sea (Katwijk-Brittenburg camp) to Vinxtbach (opposite Rheinbrohl fort on the Upper Germanic Limes), forming the border between the Roman provinces of Germania Inferior and Germania Superior. By contrast with the Upper Germanic-Rhaetian Limes, it was not marked by a solid palisade or wall. Neither can any defensive ditch or rampart be identified. The guards were stationed in nearby castra and watchtowers usually built immediately on the Rhine. The limes was served by a well-developed military road. Each camp had its own river port or landing stage and a storage area, because the Rhine not only formed the border but was also the most important transport and trade route in the region. In the first section, between the camps of Rigomagus (Remagen) and Bonna (Bonn), there were only a few camps. In the second, middle, section between Bonna and Ulpia Noviomagus Batavorum (Nijmegen), there were considerably more. Here there were also larger legion camps; with one exception, all were cavalry barracks. The landscape of the third section between Ulpia Noviomagus Batavorum and Mare Germanicum (the North Sea) was characterised by numerous small streams and boggy marshland. Consequently, in this area there was only one cavalry camp. Border security here consisted mainly of tightly packed, relatively small cohort forts.

The occupying troops, Exercitus Germaniae Inferioris, consisted mostly of auxilia cohorts. From the 2nd century, the strategic reserve comprised three legions stationed in Bonna/Bonn, Novaesium/Neuss, Vetera/Xanten and Noviomagus/Nijmegen. The control and surveillance of the waters of the North Sea, the Rhine estuary and the Lower Rhine was the responsibility of the Classis Germanica whose headquarters was in Colonia Claudia Ara Agrippinensium/Cologne. Legions, auxilia and fleet units were commanded by the respective provincial governor. From the 3rd century the ripenses (river guards), comitatenses, and liburnaria were under the command of the Dux Belgicae secundae.

Map of the Upper Germanic-Rhaetian Limes

This limes existed from the 1st to 5th centuries AD and guarded the provinces of:

• Germania Superior
• Rhaetia

It lay on the territory of the present German states of Rhineland-Palatinate, Hesse, Baden-Württemberg and Bavaria. To the north, it bordered those parts of the Roman province of Rhaetia that lay north of the Danube and guarded the eastern border of that part of Germania Superior that lay east of the Rhine. In Upper Germania the border defences initially consisted only of a post road. From about 162/63 AD, the Romans constructed a defensive barrier with watchtowers and signal towers, palisades, ditches and earthworks. On one short section of the Rhaetian Limes, a solid stone wall was erected. In its final stages, the Upper Germanic-Rhaetian Limes was about 550 kilometres long and ran from Rheinbrohl, in the county of Neuwied in northern Rhineland-Palatinate, as far as Hienheim on the Danube. Between the villages of Osterburken and Welzheim, the limes ran for 81 kilometres almost in a straight line southwards.[10] In the scholarly literature, this unusual section is considered as evidence that this type of boundary wall had never been used for defensive purposes.

The land of Agri Decumates that was guarded by this limes had to be vacated by the Romans in 260–285 AD. They moved their bases back to the banks of the Rhine and Danube, which were much easier to defend militarily. The exact route of the limes along the border between Upper Germania and Raetia has not been fully explored. In the late 4th and early 5th centuries, the Rhaetian Limes was reorganized and divided into three sections. The northern border of Rhaetia formed the pars superior (upper part), the western border was the pars media (central part) with the fortified town of Cambodunum and bases from Vemania (Isny im Allgäu) to Cassilacum (Memmingen); the pars inferior (lower part) was the section between Castra Regina (Regensburg) and Batavis (Passau).

The defending troops, Exercitus Germaniae superioris and Exercitus Raeticus, consisted mostly of auxilia cohorts. From the 2nd century, the strategic reserve was formed from three legions stationed in Mogontiacum/Mainz, Argentorate/Strasbourg and Castra Regina/Regensburg. The monitoring of the Upper Rhine was the responsibility of the Classis Germanica; that of the Rhaetic Danube came under the Classis Pannonia, whose headquarters was in Aquincum/Budapest. Legions and auxilia cohorts were under the command of the governor. From the 3rd century the Upper Germanic-Rhaetian border troops (comitatenses, repenses, and liburnaria), were commanded by three generals:

• Dux Raetiae
• Dux Mogontiacensis
• Comes tractus Argentoratensis

Location of the Roman camps on the Rhine-Lake Constance line and in the hinterland provinces of Maxima Sequanorum and Raetia I, 3rd century AD

This limes existed from the 3rd to the 5th centuries AD and guarded the provinces of:

• Germania Superior
• Rhaetia

It lies on the territory of present-day Germany, Austria, Switzerland and Liechtenstein. As early as the period 15 BC to about 70 AD, the border between Rome and Germania ran mostly along the line of the late antique Danube-Iller-Rhine Limes (DIRL) before the Romans advanced further north into the Agri decumates. Because of troop withdrawals and massive barbarian invasions, the Upper Germanic-Rhaetian Limes were abandoned in the late 3rd century and the Roman forces pulled the border back to the banks of the three rivers. Especially around the year 300, the Emperor Diocletian had new fortifications built directly on the river banks or on major roads in the hinterland here. Around 370 AD, the line of fortifications was considerably strengthened under the Emperor Valentinian I to counter the Alemanni, who were steadily advancing southwards. By contrast with the Upper Germanic-Rhaetian Limes, the DIRL primarily fulfilled defensive purposes; its camps had much stronger and higher walls than their High Imperial predecessors. Furthermore, they had in most cases been built to conform to the local topography. This meant that they could not be built in the classical 'pack of cards' shape. Between them a dense chain of watchtowers and signal towers were constructed to provide an additional security measure (burgi).

Flotillas of patrol boats were stationed on the large lakes in this region.

• Lake Constance: Numerus Barcariorum (HQ at Brigantium/Bregenz)
• Lake Neuchâtel: Classis Barcariorum (HQ at Eburodunum/Yverdon).

Comitatenses, ripenses, and liburnaria in this section of the limes were under the command of four generals:

• Dux Raetiae
• Dux provinciae Sequanicae
• Comes tractus Argentoratensis
• Dux Germaniae primae

Map of the Norican Limes

This section of the limes existed from the 1st to the 5th century AD and guarded part of the Roman province of Noricum.

It is on the soil of the present-day Austrian states of Upper and Lower Austria. It ran along the Danube from Passau/Boiodurum to Zeiselmauer/Cannabiaca. This is also a ripa (river border), which was guarded by a loose chain of cohort forts. The main road on the Norican Limes was the via iuxta amnem Danuvium. The initially simple wood and earth structures were systematically converted under Emperor Hadrian into stone encampments. During the 4th century, they were brought once more up to date and massively reinforced. Between the camps, in strategic places or good points of observation, were watchtowers or signal towers and, in the Late Antiquity, burgi. In the middle section, between the camps of Favianis and Melk, watchtowers were built only sporadically. Here the narrow valley of the Wachau, with its densely forested escarpments, made access to the riverbank more difficult, providing some defensive function. Every camp had its own river port or landing stage and a storage area because the Danube was not only a border zone, but also the most important transport and trade route in the region. Over time civilian settlements or vici were established immediately next to the camps. In the immediate hinterland of the limes, walled towns or municipia were founded – for example, Aelium Cetium or Ovilava (Wels). They were the administrative or commercial centres of the region. In late antiquity, the Norican area was divided into two parts (pars inferior and pars superior).[11] It is probable that a second, defensive line was created to the rear (Castrum Locus Felicis).

The occupying troops, Exercitus Noricus, consisted mostly of auxilia cohorts and a legion stationed in Lauriacum/Enns acted as the strategic reserve. The surveillance and security of the Danube and its tributaries were the responsibility of the Classis Pannonia. Units of the legions, naval and auxiliary forces were commanded by the respective governors. In late antiquity – according to Notitia Dignitatum – four newly established flotillas undertook this task. From the 3rd century, the Norian comitatenses, ripenses and liburnari were under the command of two generals:

• Comes Illyrici
• Dux Pannoniae Primae et Norici Ripensis

Map of the Pannonian Limes with its perimeter defences

This stretch of limes was in use from the 1st to the 5th centuries AD and helped to guard the provinces of:

• Pannonia inferior
• Pannonia

The Pannonian Limes is situated on the territory of present-day Austria, Slovakia and Hungary. Although this section of the frontier was relatively well protected by the Danube river border or Ripa, the Roman military presence here was always exceptionally strong (three military camps in Pannonia, but only one in Lower Pannonia) because especially after the abandonment of Roman Dacia in the late 3rd century, the pressure of migrant peoples from the east on this section of the limes intensified. The tributaries emptying into the Danube offered cheap transport routes, but also made good approach routes for invaders and raiders. The military camps were therefore built by the most important fords or confluences and road termini. The legion- and auxilia camps were mainly located in the immediate vicinity of the riverbank. The initial wood and earth structures, were systematically converted under Emperor Hadrian into stone barracks and, in the 4th century, redesigned and massively strengthened in order to match new strategic requirements. The gaps between the camps were closed by a chain of watchtowers or signal towers. In late Roman times huge inland camps were built and towns in the hinterland were fortified to create a second line of defence. In addition, at vulnerable points, units of the Danube fleet were stationed. In the time of Emperor Marcus Aurelius the first mention is made in Pannonia of stone watchtowers (burgi, panelled towers and fortlets (praesidia). In late antiquity, the Pannonian military district was divided into two parts (pars inferior and pars superior).[11] Advance defences were provided by bridgehead camps (e.g. Castra Contra Aquincum or Celemantia) and military stations on main transport routes in the Barbaricum (e.g. near Musov).

Black lines indicating the approximate path of the 4 sections of the Fossatum Africae

Fossatum Africae ("African ditch") is a linear defensive structure (limes) that extended over 750 km or more[17] in northern Africa constructed during the Roman Empire to defend and control the southern borders of the Empire in the Roman province of Africa. It is considered to have many similarities of construction to Hadrian's Wall at the northern border of the Empire in Britain. Generally the Fossatum consists of a ditch and earth embankments on either side using the material from the ditch. Sometimes the embankments are supplemented by dry stone walls on one or both sides; rarely, there are stone walls without a ditch. The width of the Fossatum is generally 3–6 m but in exceptional cases may be as much as 20 m. Wherever possible, it or its highest wall is constructed on the counterscarp. Excavations near Gemellae showed the depth there to be 2–3 m, with a width of 1 m at the bottom widening to 2–3 m at the top.[18]

The Fossatum is accompanied by many small watchtowers and numerous forts, often built within sight of one another.

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UNESCO World Heritage sites in Northern England: 1–2 = Hadrian's Wall, 3 = Aesica aqueduct, 4 = Corstopitum

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UNESCO World Heritage sites in Scotland: 1–2 = Antonine Wall, from Old Kilpatrick to Bo'ness

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UNESCO World Heritage sites in Germany: 1–2 = Limes Germanicus, from Rheinbrohl to Eining