The Blockhaus d'Éperlecques is a Second World War bunker, now part of a museum, only some 14.4 kilometers north-northwest from the more developed La Coupole V-2 launch facility, in the same general area.
The bunker, built by Nazi Germany under the codename Kraftwerk Nord West (Powerplant Northwest) between March 1943 and July 1944, was originally intended to be a launching facility for the V-2 (A-4) ballistic missile. It was designed to accommodate over 100 missiles at a time and to launch up to 36 daily.
The facility would have incorporated a liquid oxygen factory and a bomb-proof train station to allow missiles and supplies to be delivered from production facilities in Germany. It was constructed using the labour of thousands of prisoners of war and forcibly conscripted workers used as slave labourers.
The bunker was never completed as a result of the repeated bombing by the British and United States air forces as part of Operation Crossbow against the German V-weapons programme. The attacks caused substantial damage and rendered the bunker unusable for its original purpose. Part of the bunker was subsequently completed for use as a liquid oxygen factory. It was captured by Allied forces at the start of September 1944, though its true purpose was not discovered by the Allies until after the war. V-2s were instead launched from Meillerwagen-based mobile batteries which were far less vulnerable to aerial attacks.
Today, the bunker is preserved as part of a privately owned museum that presents the history of the site and the German V-weapons programme.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.