The Great Anastasian wall of the Byzantines.
The unknown Αnastasian wall. The 2nd largest wall in European history
We all more or less know about the Theodosian walls of Constantinople. Rarely, however, will we find in history books a reference to the 56 km wall of Anastasios.
To understand the sizes: With such a one can, approximately, cover the whole of Attica to the north from the Evian to the Corinthian gulf.
This is what Europe has to show closest to the Great Wall of China (along with, of course, the 117 km of Hadrian's wall).
It was five meters high and 3 meters wide. It had towers and a moat in front. In the middle there was a large rectangular castle 250x300 m. Today, unfortunately, few things survive.
It was created with the need to protect the rich and crowded suburbs of Constantinople that were outside the Theodosian walls. Indicative: Region (Kücükçekmese), Seventh (Bakirköy), Syka (Galatas), Ag. Mamas, Source (Balikli), Dripia (Ataköy), Sosthenion (Istinye), Rides (Selimpasa)
The wall was eventually abandoned because it had limited effectiveness.
For example, even in the strong days of Justinian, in 558 AD, 7000 Kutrigur * horsemen (as a mass think that Theoden is coming with all the Rohirim above you) broke the wall and were found 10 km away from Chrysi Gate.
* Proto-Bulgarian, Turkish tribe. 2000 of them settled permanently with their families in Thrace. As soldiers of the Roman army, they stood out in the famous battle of Ad Decimum in present-day Tunisia (Recapture of Carthage by the Vandals)