The Atlantikwall (Atlantic Wall) was an extensive system of coastal defences and fortifications built between 1941 and 1944 by Nazi Germany. It was intended as a defence against an anticipated Allied invasion of Nazi-occupied Europe from the United Kingdom. Hitler ordered the construction of the fortifications in 1942 through his Führerbefehl No. 40. They used slave labour, in France alone more than a half million French workers were drafted to build it. The wall extended from the Spanish border in France through Belgium and the Netherlands, Germany and Denmark to Norway. There are 8119 along the length of 2685 km. The fortifications included colossal coastal guns, batteries, mortars, and artillery. The manning and operation of the Atlantic Wall was administratively overseen by the Wehrmacht. Thousands of German troops were stationed in its defences.
The construction was made using a sort pre-fabricated plan. The Regelbau (standard build) system used a catalog of 600 approved types of bunker and casemates. Standard features were an entrance door at right angle, armoured air intake, 30-millimetre steel doors, ventilation and telephones. For this reason there were over 200 standardized armour parts. The standardization greatly simplified the manufacture and increased the speed of construction. Much of Europe became a sort of Atlantikwall-factory.
France was closest to Great Britain, so the invasion was expected to land somewhere at the norther coast of France and probably Belgium. As a result the fortifications in this area had the highest priority. Nevertheless, the Atlantikwall was never fully completed. And while it cost a lot of lives of the landing soldiers on D-Day, it actually could not change the outcome.
After the war, there was little interest in preserving the wall. Some beach fortifications collapsed or were eaten by erosion and the remains are now underwater. Some were removed by later constructions, for example industrial areas of housing. Others were demolished because they became a threat. But most simply decayed. There was a discussion whether France should declare the wall a National Monument, but no government so far has envisaged this. Nevertheless, some of the most spectacular fortresses have been preserved by non-profit associations for their historic importance and are now open to the public. In general, they are a museum and also host exhibitions on the war and the local history during the war.