The ancient world’s largest fortresses: Persia’s northern defences in late antiquity

In the 4th to 6th centuries AD, Persia was under attack from the north by the ‘White Huns’ and other powerful groups of steppe warriors. Persia’s response was to create a massive fortification belt – unsurpassed in scale anywhere in the ancient and medieval world, with only the possible exception of China. Eberhard Sauer, Jebrael Nokandeh, Hamid Omrani Rekavandi, Mohammadreza Nemati, and Mehdi Mousavinia have explored the backbone of the system: the densest concentration of mega-fortresses in the late antique world, in the Gorgan and Tehran Plains of Iran.

Who built the ancient world’s largest fortresses? Many would probably point to the Roman army as the likely answer. Its legionary fortresses cover on average 15-25ha, while Britain’s largest Roman fortification – a temporary camp erected to protect a campaigning army – reached a size of 70ha. After the 3rd century AD, however, Rome ceased to erect well-entrenched camps, and late Roman legionary fortresses shrank to as little as 5ha in size. But even the largest Roman military compounds are dwarfed by Persian fortresses, which have a footprint of up to c.200ha – a size that is only reached elsewhere in the ancient world by cities or thinly occupied hilltop refuges. Yet not all of Persia’s giant geometric fortresses were cities. Instead, some sheltered vast armies living in tents. These fortifications contained no urban amenities or dwellings, and were accessible only via heavily guarded and narrow zigzag gateways. Why, then, were such exceptional fortifications constructed in late antique Persia?

From the 3rd century AD to the rise of Islam in the 7th century, Persia was ruled by the Sasanian dynasty. From the first decades of Sasanian rule, Persia proved capable of inflicting defeats on Rome, took major cities by storm and erected a siege camp at Hatra in Iraq, which is more than twice the size of any known Roman camp. Thanks to its military feats, the Persian Empire expanded to the Caucasus passes in the north and the River Indus in modern Pakistan in the east.

The Near East is the place to look for the ancient world’s largest fortresses. Here we see Qal‘eh Iraj, which – at 187ha in size – is one of the largest non-urban fortresses in the Sasanian Empire. This drone image was taken by Davit Naskidashvili as part of the joint project.

It was in the 4th century that the Huns and related groups moved westwards from central Asia. Sasanian and Roman territories came under attack from these northern steppe warriors and other ethnic groups pushed out of their former domiciles. The onslaught caused Germanic tribes to migrate to Roman territory, forcing the Western Roman Empire to shrink in size and eventually cease to exist. How did Persia, closer to the epicentre of these large-scale population movements of the Migration Era, face up to the challenges that annihilated Western Europe’s dominant power? The answer included the construction of impressive fortifications, including both strongholds and great long walls, on its northern frontiers.

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