The Danube Limes - Protecting the Roman Balkans

Reconstruction of a Limes tower in Germany.

The First Line of Defense - The Limes

A limes was a border defence or delimiting system that marked the boundaries of the Roman Empire.

The Latin noun limes had a number of different meanings: a path or balk delimiting fields, a boundary line or marker, any road or path, any channel, such as a stream channel, or any distinction or difference. In Latin, the plural form of limes is limites.

The word limes was utilized by Latin writers to denote a marked or fortified frontier. This sense has been adapted and extended by modern historians concerned with the frontiers of the Roman Empire: e.g. Hadrian's Wall in the north of England is sometimes styled the Limes Britannicus, the frontier of the Roman province of Arabia facing the desert is called the Limes Arabicus, and so forth.

It would be a misunderstanding that there ever was one limes system of defense. There was a difference between the solid limes of Britain ("Hadrian's Wall"), and the more open system of forts in Syria. Still, there are some similarities. 

The most important one is the easiest to ignore: the grand strategy of the empire was, on the whole, defensive. The Sahara, Euphrates, Danube, and Rhine were natural frontiers, and it was exceptional when the Romans launched new campaigns of conquest. If territory was added, it was to shorten the frontier, or to improve a vulnerable part of the frontier. The exception that proves the rule is Trajan's conquest of Dacia.

The basic principle of defense was deterrence: wherever the enemy attacked, he would always find a professional, heavily armed Roman force that often outnumbered him. Except for the desert frontier, the limes usually consisted of a clear line where the enemy had to stay away from (e.g., Hadrian's Wall or the river Danube).

However, sometimes the line was attacked. The soldiers in the watchtowers signaled the invasion to the nearby forts. The watchtowers themselves were lost, but the invaders would immediately have to face with Roman forces from nearby forts.

Almost always, this was sufficient to deal with the situation. If the attackers were able to reach and loot a city, they would be massacred on their way home. The final act of every attempt to attack the empire was Roman retaliation against the native population.

A combination of force and diplomacy was used to control the border. 

Photo: Danube Limes Project

Think of the word "Porous"
The Danube Limes was not a solid wall defending the Empire's frontier.  Rather it a was a series of fortified cities, small forts and watchtowers.  The Limes was porous with assorted invading Slavs, Huns or Avars pouring through on raids dedicated to looting or conquest.  In theory the Roman/Byzantine strongpoints would slow down invaders allowing for troops stationed close by to push the enemy back over the border. 

The Danube Limes

The frontier of the Roman Empire, from the Danube to the Black Sea, played a crucial role in making and breaking emperors and protecting Roman society along its course.

Along the Danube from Bavaria to the Black Sea there is a frontier system with fortresses and fortlets built by the Roman army such as Carnuntum (Austria), Aquincum (Budapest, Hungary), Viminacium (near Belgrade, Serbia) or Novae (Svistov, Bulgaria). Together with hundreds of watchtowers and large urban settlements they are part of an impressive military machine.

The river itself was the most dominant element of the frontier system, used as a demarcation line against the Barbarian world to the north and as a fortified transport corridor.

The forts, situated mostly on the right side of the river, acted as check-points to control traffic in and out of the empire. Their ruins, above and below ground, visible or non-visible, are often in remarkable shape and well integrated in the landscape.

Some of the early Limes defenses were built in the early Empire period.

• 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

The fall of the Western Empire impacted the ability to man the Danube Limes to a degree.  But the Eastern Empire still needed to defend their Balkan borders from invading tribes.

In the east the original Roman Limes system would slowly melt away.  It would be replaced by an Eastern Roman line of fortified towns and strongpoints.

The Byzantines struggled for centuries to maintain anything like a recognizable Balkan border.  Invading tribes from Central Asia were constantly pouring over the Danube River and conquering Roman territory all the way down into Greece and up to the walls of Constantinople itself.

The Byzantines sometimes saw their strongpoints fall almost as fast as they could be built.  A truly permanent Limes system was rare.  But a system of fortifications of one kind or another was used through 1204.

The Limes Fortress of Novae
The legionary fortress in Novae (modern Bulgaria) on the Danube River. The fortress, the same as other military bases, was surrounded by the civilian settlement (canabae) which constituted with its camp a specific settlement structure. Topography and planning of settlements of this kind is not well-recognized, since only a few have been excavated so far, mainly in the western part of the Empire.

Fortress of Novae
The Roman military fortress at Novae was established in AD 45 (46) by Legio VIII Augusta. The Legio I Italica was stationed there in AD 69 and until the second quarter of the 5th century AD Novae was its main camp. Up until now within the camp have been investigated the headquarters of the legion, one of the residences of the senior officers – the tribunes, the military hospital and the legion’s thermae, upon which the episcopal complex was erected in the second quarter of the 5th century AD.
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In the late 5th and 6th centuries Novae was a bishopric. The cathedral and neighbouring buildings were built west of the former legionary headquarters. The last period of prosperity was during the reign of Justinian (527-565) when the defensive walls were rebuilt and reinforced. The town existed until the early 7th century AD, when it was destroyed by the attacks of Avars and Slavs.

Roman Limes:

Frontier line of the Roman Empire in the Iron Gate area

By Vladimir Kondić
Former director of the Institute of Archaeology of the Serbian Academy of Sciences and Arts.  Below are a few excerpts from the much longer article that apply to the Byzantine period.


Although it is very probable that Valentinian and Valens undertook reconstruction work on a larger scale because of the Gothic threat, the archaeologically most noticeable phase is the period of horrible destruction and fire immediately following the battle of Harianople. But, basic fortification elements like walls, gates, and lowers remained almost unchanged.

In the following period, under new conditions, when units of foederati protected the frontier, all the ruins were filled in and levelled, making a platform where the limitanei built the wattle and daub homes which are so evident at Pontes and Diana. This period in the history of the frontier lasted until the middle of the fifth century. Thanks to the fortunate discovery of five solidi (the latest an issue of 443) of Theodosius II we know the exact termination date of the Iron Gate Roman limes.

The Huns’ invasion from the direction of Niš (Naissus) caused such destruction that Procopius correctly described the situation as disastrous. Fortifications were razed to the ground, and at Diana the south wall with its gate and the fourth-century porticoed building were destroyed. Thick layers of burnt rubble, building debris and ash covered most of the fortress and mark the end of the five centuries of its existence. Other fortresses suffered a similar fate. This period was the terminal phase of the restored, late Roman limes and the northern frontier of the empire. The final renaissance of the Danubian limes occurred under Justinian I.

The significant testimony of Procopius concerning the renovation and reinforcement of the Danubian frontier has been confirmed in its entirety by our recent archaeological research.

Procopius paid considerable attention to construction work on the Iron Gate frontier (limes) and provided at times rather detailed information about the former Roman frontier. The sequence in which he comments on the fortifications in those sectors which have been investigated make it possible to identify the Roman and early Byzantine toponyms for some sites whose ancient names were not known previously (e.g. Kantabaza, Smyrna, Campsa).

Furthermore, excavations in the Iron Gate gorge have demonstrated that Justinian’s builders in the early Byzantine period entirely retained the disposition of fortifications from the former Roman frontier. Some elements of the earlier Roman castella were altered, most likely because of the requirements of a new defensive strategy, and at locations which were in greater danger because of their topographic circumstances completely new fortifications were constructed. Now it is possible with complete certainty to reconstruct the composition of the Justinianic limes on this part of the Danube.

The fortresses can be divided typographically into the following groups:

1. Renovated Roman auxiliary and other minor forts.
2. Renovated late Roman burgus – forts (from the Diocletian and Constantine periods).
3. New early Byzantine forts built around renovated late Roman burgus-forts.
4. Completely new early Byzantine forts.

After the Huns’ invasion in 443 AD damages to the forts were not repaired until the early sixth century, which for this sector of the Danubian limes is the only period devoid of any traces of activity. Then in the early Byzantine period all the auxiliary bases on the limes were renovated. The former Roman forts for the most part were renovated on the basis of their original plans. The most frequent alterations which can be observed are the closing-off of gates. These were either walled up or replaced by large rectangular or circular towers. Usually the corner towers were completely rebuilt.

At the fortress Diana (early Byzantine Zanes) at the southeast corner a new tower was built in a horseshoe-shape with an apsidal termination, and two fortification walls were joined together in a point to form a type of bastion. The southern wall and gate, which had been razed to their foundations by the Huns, were rebuilt in exactly the same plan as before and the gate remained the only one in use. In the interior of the fortress, without any type of regular disposition, buildings of wood, earth and courses of poorly joined stones were erected.

At Novae (early Byzantine Nobas) the former Roman south gate was completely closed-off and new circular towers were built in place of the earlier east and west gates. All the towers in this fortress were built afresh, with circular plans. The situation is similar at other forts. Everywhere fortification walls were significantly reinforced, most often from the inside. At the former Roman quadriburgium Campsa, the alterations were somewhat more radical. The south gate was closed-off and two new U-shaped towers were added there. Additionally, all of the auxiliary bases contained solidly built, single-nave churches.

Reconstruction of a Limes strongpoint.

The second category of renovation was the least complicated. The Diocletian-Constantine period castella received reinforced fortification walls (cc. one meter thick), and new entrances without towers, features not previously present in these complexes, were constructed. Certainly the most interesting form of renovation consisted of the erection of completely new and characteristically early Byzantine fortification walls around the former burgi. In these situations the renovated burgi functioned as watch towers.

Two outstanding fortifications of this type are Glamija and Donje Butorke. The latter has a more complex plan, with piers on two of the towers and one rectangular tower with an apsidal termination. This type of fortification recalls in a certain sense an inaccurate statement of Procopius (De Aedificiis, 4.1) in which he states that Pincum, Cuppae, and Noveae were formerly only Roman towers around which Justinian caused buildings to be erected and to which he granted municipal status after their defenses were strengthened. As mentioned above, during the Roman period civilian settlements of a type which did not exist in Justinian’s time developed around the auxiliary bases. Could it be that Procopius in his exaggeration of credit to the emperor actually had in mind the construction of new fortresses around earlier Roman towers?

Finally, the last group consists of purely Justinianic castella which were completely new constructions. Up to date six of these have been discovered on the Iron Gate section of the limes. Saldum (Kantabaza) in plan is an irregular rectangular with three circular towers and a single elongated one with an apsidal termination. The fort at Bosman is the only complex with a triangular plan on this part of the Danube and is skillfully into the restricted space between the mountain range and the river. The eastern fortification wall, located right on the river, was laid out in a convex line so that high water levels on the river would not be able to damage it seriously.

The fort at Hajdučka Vodenica was constructed on the site of an earlier tower which was not renovated in the sixth century. It is situated high on the river bank, and from each and of its northwest perimeter wall extends a fortification wall with a tower at its end to protect a small river harbour. The forts at Milutinovac and at the mouth of the Slatinska river are very similar in both construction and size (55 x 55 m.). They are defended by circular towers with square foundations on defensive walls which are turned toward the river and form the foundation for an upper-level entrance.

In almost all of the fortresses of Justinian time one layer of ash and destruction debris can be observed which can be dated to 580 AD when a forceful Slavic incursion on this part of the Danube was recorded. However, the fortresses themselves did not experience such significant destruction that they could not be once again renovated after the passage of that crisis. However, even this strong system of fortifications could not withstand a disastrous attack by combined forces of Slavs and Avars in 596 AD, and it was then that the Justinianic limes was definitively destroyed.

Full article

Castra Capidava, Romania
During the 2nd and 3rd century AD a Roman fort was built in the area, later overbuilt by a Late Roman fort, which lasted from the 4th to the 6th century AD.  The fort functioned as a guard of the Danube River and ford. At the banks of the Danube a massive harbour wall, 2.50 m thick and 60 m long, was found.
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The fortified settlement played an important role in the Roman defensive system belonging to the series of camps and fortifications raised during the reign of Emperor Trajan, in the early 2nd century, as part of the measures to organize the Danubian limes. Capidava being part of the Limes Moesiae.  Destroyed by Goths in the 3rd century, the fortifications were rebuilt in the next century. 
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Sources between the 4th to 6th centuries talk about cavalry units.  The fort was abandoned in 559 after the invasion of the Cutriguri.  the city was rebuilt by the Byzantines in the 10th century.  In the spring of 1036, an invasion of the Pechenegs devastated large parts of the region, destroying the forts at Capidava and Dervent and burning the settlement in Dinogeţia.

Fortress of Viminacium
Viminacium, in modern Serbia, was a major city and military camp and the capital of Moesia Superior.  The city dates back to the 1st century AD, and at its peak it is believed to have had 40,000 inhabitants, making it one of the biggest cities of that time. It lies on the Roman road Via Militaris.
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Viminacium was devastated by Huns in the 5th century, but was later rebuilt by Justinian. It was completely destroyed with the arrival of Slavs in the 6th century. Today, the archaeological site occupies a total of 450 hectares (1,100 acres), and contains remains of temples, streets, squares, amphitheaters, palaces, hippodromes and Roman baths.



Roman Balkans in the 6th century.
Click to enlarge.

The Eastern Romans faced invasion by an endless series
of tribes pouring in from Central Asia.

(Borders of the Roman Empire)      (livius.org)      (Limes)

(castrumandquonset)      (provinces.uw.edu)      (icpdr.org)

(danube-cooperation.com)      (latvany-terkep.hu)      (danube-limes)

(danubelimesbrand.org)      (bnr.bg/en)      (historyfiles.co.uk)