The Long Walls of Thrace were comparable to Hadrian’s wall which is a more famous Roman construction of similar purpose. They were designed to protect the hinterland of Constantinople from raiding by barbarians as the military situation became increasingly unstable, though they were not used after the early history of the Eastern Roman Empire. The walls were about 65km west of Constantinople. The walls ran 45km from the Black Sea to the Sea of Marmara, an extremely large wall. Large stretches of the wall still exist, most of the foundations still exist either above or above ground today. The wall had a ditch in front of it, and it had a system of forts just as Hadrian’s Wall did.
AN IMPRESSIVE WALL WHICH DESERVES MORE STATUS:
According to historian J.G. Crow – “as it survives, it is the most monumental linear fortification dating from antiquity in continental Europe, comparable only with Hadrian’s Wall in its complexity and preservation. Yet compared with the Roman Wall in Britain almost nothing is recorded of the structure of the Long Walls and there has never been a detailed survey or excavation.” It was constructed not with alternate layers of stone and brick, the same construction technique used on the walls of Constantinople, but instead with limestone bricks with a hard lime mortar core. However, it is possible such a large wall was not constructed uniformly. The different numbers, shapes, and spacing of the towers are indications the wall had been constructed and reconstructed in multiple phases.
How were the Long Walls used?
The purpose of the Long Walls was defense of the area surrounding Constantinople, but how they were used is not abundantly clear from the sources we have. The historian J.G Crow wrote that there are a “variety of forts and camps which are known to be associated with the Long Walls…The Long Walls as a system clearly underwent a series of changes and modifications throughout their history, but whatever the comments of contemporary or later historians the evidence of the camps and forts clearly demonstrates that at certain periods at least the walls were held and garrisoned by a permanent force.”
The size of the army garrisoning the Anastasian wall is not mentioned in the primary sources, however Crow theorized that based on other garrisons and a comparison to Hadrian’s wall that it had approximately 3,825 men stationed to defend it. That is just a calculation, but perhaps it is the best general idea we can have with the information possessed. Needless to say, the Long Walls did not last for long as an important layer of defense. The walls clearly fell out of common use by at least the 7th century as the Romans no longer had the ability to garrison such a long wall permanently. By then Constantinople was a proven defensive point which faced no credible threat from the Byzantine’s Balkan enemies.
HOW DID THE WALLS FIT INTO BYZANTINE STRATEGY:
The need for Balkan defenses began to seriously increase in the Fourth Century, in particular after the large-scale defeat by the Goths at the Battle of Adrianople in 378. The sources do not specifically say that there was this strategic change, but the Roman Empire clearly began to make changes towards that aim. The Romans began fortifying strategic passes such as Thermopylae and the Isthmus of Corinth, which were vast distances from the Danube border. This shows that the Romans had expectation that enemies would be marching through their territory and that the field armies would not always be able to defeat them. The Empire fortified the Bosphorus and the Hellespont to prevent any barbarians from moving into Anatolia, which the Gothic leader Gainas attempted in 400 or 401. In the early 5th century Constantinople added the Theodosian walls which was the most important of these defensive adaptations. After seeing the Vandals sack Rome in 455, and the fact they had naval power, Constantinople was fortified with a set of sea walls as well. Thessaloniki’s walls were fortified at this time as well. Only serious concern for the safety of the Balkan provinces would have resulted in such serious spending, and the Long Walls were another example of that.
The Danube frontier was still active, Prokopios wrote in his work Buildings: “Wishing as he did to make the Danube the strongest possible line of first defence before them and before the while of Europe, he distributed numerous fortifications along the bank of the river, as I shall describe, and he places garrisons of troops everywhere along the bank to check for the crossing of the barbarians.” This is an admission that the Danube was not secure even during Justinian’s reign, and more of a way to check on the movements of the barbarians, prevent small incursions, and harass them. There were no secure borders in the Roman Empire, it was defense in depth.
The Long Walls were the last line preventing an attack on Constantinople if the Danube was the first line. The defenses do seem to have worked in the 5th and 6th centuries when they were actually manned by a proper garrison, but as soon as they weren’t they were useless. Another problem was the enemies of the Romans got stronger. If an enemy had siege engines, as the Avars did in 626, how could a small army defend a 45km wall? The answer is they had no chance. After the reign of Heraclius and the Avar siege of 626, the Romans no longer maintained wall. It was not going to stop Avars or Bulgars. After that, the Romans relied on the walls of Constantinople and Thessaloniki as their places of refuge in the Balkans.
This article was written with an excellent paper from the following work: Constantinople and its Hinderland: Papers from the Twenty-seventh Spring Symposium of Byzantine studies, Oxford, April 1993. #9 “The Long Walls of Thrace” by J.G Crow (pages 109-124)
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