German World War II fortresses

German fortresses during World War II (German: Festungen or Fester Platz, lit. 'fixed place'; called pockets by the Allies) were bridgeheads, cities, islands and towns designated by Adolf Hitler as areas that were to be fortified and stocked with food and ammunition in order to hold out against Allied offensives. The fortress doctrine evolved towards the end of World War II, when the German leadership had not yet accepted defeat, but had begun to realize that drastic measures were required to forestall inevitable Allied offensives.

Source: Wikipedia — German World War II fortresses (CC BY-SA 4.0)