The famous Maginot Line was built in France during the 1930s and runs parallel to Germany. It was designed to defend France from further aggression from the East. The first section of the line was built along the Southeastern border of France to shield from rising fascism in Italy and later, the construction began along the German border. The fortresses have interlocking fire, but are not connected with each other. The thought process behind the was that the batteries could fire on each other if the one was being overrun and interconnecting tunnels would be dangerous because an enemy could take one fortress and then go through the tunnels to the rest. Some of the complexes are absolutely amazing. We have the third largest fortress in the line about 35 km from us located near the French town of Bitche.