The borders or the frontiers of the Roman Empire, were a combination of natural frontier and man-made fortifications which separated the lands of the empire from the “barbarian” countries beyond. It stretched over 5,000 km from the Atlantic coast of northern Britain, through Europe to the Black Sea, and from there to the Red Sea and across North Africa to the Atlantic coast.



Also known as “the limes”, it was a border defence or delimiting system of Ancient Rome. It marked the boundaries of the roman empire at its greatest extent in 2nd centruy. The word limes was utilized by Latin writers to denote a marked or fortified frontier. So basically limes was a boundary. The remains of the limites (plural) today consist of vestiges of walls, ditches, forts, fortresses and civilian settlements. The remains of the Limes today consist of :

  • vestiges of built walls
  • ditches
  • forts
  • fortresses,
  • watchtowers
  • civilian settlements.


Some of the famous limites were:

  • Hadrian’s Wall, also known as Limes Britannicus
  • Antoinie Wall– in Scotland
  • Limes Germanicus, the Germanic and Raetian Limes
  • Limes Arabicus,  the frontier of the Roman province of Arabea Petrecea (facing the desert)
  • Limes Tripolitanus, the frontier in modern Libya facing the Sahara
  • Limes Alutanus,  the eastern border of the Roman province of Dacia
  • Limes Transalutanus, the frontier in the lower Danube
  • Limes Moesiae, the frontier in eastern Romania and Moldavia
  • A medieval limes is the Limes Saxoniae in Hostel


The limes was a cross-path or a cross-wall, which the Romans meant to throw across the path of invaders to hinder them. It is a defensive strategy. The Romans never built limites where they considered themselves free to attack. As the emperor had ordered the army to stay within the limites except for punitive expeditions, they were as much a mental barrier as material.

Roman writers and subsequent authors who depended on them presented the limes as some sort of sacred border beyond which human beings did not transgress, and if they did, it was evidence that they had passed the bounds of reason and civilization. To cross the border was the mark of a savage.



Individual fortifications had been constructed by the Roman Military from as early as the building of Rome’s first city walls in the 6th or 7th century BC. However, systematic construction of fortifications around the periphery of the empire on a strategic scale began around 40 AD under Emperor Caligula.

However, it was under Hadrian’s rule, which began in 117, that the Roman frontier was systematically fortified. He spent half of his 21 year reign touring the empire and advocating for the construction of forts, towers, and walls all across the edges of the empire.

The limes consisted of fortresses for legions or vexillations (e.g. Segendenum) as well as a system of roads for the rapid transit of troops and, in some places, extensive walls. Perhaps the most famous example of these is in Great Britain, which was built across the entire width of the island to protect from attack from tribes located in modern-day Scotland.



However, it is not correct to interpret other limes in the same way or to view the limes as an impenetrable barrier. Fortifications as impressive as Hadrian’s Wall were not unbreachable: with milecastles some distance apart and patrols infrequent, small enemy forces would have been able to penetrate the defenses easily for small-scale raiding. However, a raiding party would be forced to fight its way through one of the well-defended gates, abandon its loot, such as cattle, thus negating the whole purpose of the raid or be trapped against the wall by the responding legions. Additionally, a large army would have been able to force a crossing of the limes using siege equipment. 

The value of the limes lay not in its absolute impenetrability but, as S. Thomas Parker argues, in its hindrance to the enemy: granting a delay or warning that could be used to summon concentrated Roman forces to the site. The limes are therefore perhaps better seen as an instrument allowing a greater economy of force in defense of a border than otherwise would be necessary to provide the same level of defense.

After 270, the maintenance of an impenetrable solid frontier was abandoned by Constantine I in favor of a policy, whether deliberate or forced by circumstance, of “defense in depth”. This called for the maintenance of a softer, deeper perimeter area of defense, with concentrated hard points throughout its depth. The idea was that any invading force of a sufficient size could penetrate the initial perimeter but in doing so with any element of surprise or rapid movement would be forced to leave several defended hard points (fortresses) to its rear, hampering its lines of supply and communications, and threatening surrounding of the force.

In the very late Empire the frontiers became even more elastic, with little effort expended in maintaining frontier defense. Instead, armies were concentrated near the heart of the empire, and enemies allowed to penetrate in cases as far inwards as the Italian peninsula before being met in battle.

In the Northern Fortifications, called the Limes Britannicus, the average garrison of the wall fortifications is thought to have been around 10,000 men. Along with a continuous wall (except in the case of Gask Ridge), there existed a metaled road immediately behind the wall for transport of troops. Along the wall there existed a few large forts for legions or vexillations, as well as a series of milecastles – effectively watchtowers that were unable to defend a stretch of wall against anything but low-scale raiding but were able to signal attack to legionary forts by means of fire signals atop the towers.

A series of naval forts was built along the south east coast, initially to combat piracy but later to protect from raiding and the threat of invasion from Saxons that eventually led to the Saxon occupation of Lowland Britain by 600 and is reflected in the name of the fortification system: the Saxon Shore, which extended to the northern coasts of France. Each shore fort both protected against direct attack and also sheltered a small naval sub-fleet of vessels that could patrol the coast against pirates and raiders.




After conquering much of the modern landmass of Great Britain, the Romans halted their northern expansion at the southern fringe of Caledonia, what is now central Scotland. This left them with a border shared with a people who made repeated raids and insurrections against them. Unlike other borders throughout the empire, there was no natural border to fall back on such as desert or wide river that crossed the whole peninsula, so instead a series of defenses were built in southern to mid-Scotland in order to protect the province of Britannia from the Caledonians and later the Picts

Although the border was not a continuous wall, a series of fortifications known as Gask Ridge in mid-Scotland may well be Rome’s earliest fortified land frontier.Rather than representing a series of consecutive advancements, the border should be seen as fluctuating – the Antonine Wall for example was built between 142 and 144, abandoned by 164 and briefly re-occupied in 208.

Continental Europe

In continental Europe, the borders were generally well defined, usually following the courses of major rivers such as the Rhine and the Danube. Nevertheless those were not always the final border lines; the province of Dacia, modern Romania, was completely on the far side of the Danube, and the province of Germania Magna, which must not be confused with Germania Inferior and Germania Superior, was the land between the Rhine, the Danube and the Elbe(although this province was lost three years after its creation as a result of the Battle of Teutoburg Forest)

 It consisted of:

  • The Lower (Northern) Germanic Limes, which extended from the North Sea at Katwijk in the Netherlands along the Rhine;
  • The Upper Germanic Limes (just to be confusing, also called the Rhaetian Limes or simply “the Limes”) started from the Rhine at Rheinbrohl (Neuwied (district)) across the Taunus mountains to the river Main (East of Hanau), then along the Main to Miltenberg, and from Osterburken (Neckar-Odenwald-Kreis) south to Lorch (Ostalbkreis) in a nearly perfect straight line of more than 70 km;
  • The proper Rhaetian Limes extended east from Lorch to Eining (close to Kelheim) on the Danube. The total length was 568 km (353 mi). It included at least 60 castles and 900 watchtowers.
  • In Dacia, the limes between the Black Sea and the Danube were a mix of the camps and the wall defenses: the Limes Moesiae was the conjunction of two, and sometimes three, lines of vallum, with a Great Camp and many minor camps spread through the fortifications


The eastern borders changed many times, of which the most enduring was the Euphrates river, bordering the Parthian Empire in modern Iraq and western Iraq. Rome advanced beyond the Euphrates for a time upon defeating their rivals, the Parthians in 116 AD, when Trajan captured Ctesiphon, and established new provinces in Assyria and Babylonia. Later that year he took the Parthian capital,Susa, deposed the Parthian King Osroes I. However, the Romans did not Romanize the entire Parthian Empire, leaving Parthamaspates a puppet king on the throne to rule over former Parthian lands with the exclusion of modern Iraq, which became Assyria and Mesopotamia


At its greatest extent, the southern borders were the deserts of Arabia and the Sahara, that represented a natural barrier to prevent expansion. The Empire controlled the Mediterranean shores and the mountains opposite. However the Romans attempted twice to occupy effectively the Siwa Oasis (and failed) and controlled the Nile many miles into Africa until the 1st Cataract near the modern border between Egypt and Sudan.

For Mauretania there was a single wall with forts on both sides of it. In other places, such as Syria and Arabia Petraea, there was instead a network of border settlements and forts occupied by the Roman army.

  • Limes Arabicus (called the Limes Uranus) was the frontier of the Roman province of Arabia Petraea facing the desert.
  • Limes Tripolitanus was the frontier in modern Libya facing the Sahara.


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