The complex was protected by circa four meters of concrete. About 30 small rooms were distributed over two levels with exits into the main buildings and an emergency exit into the garden. The complex was built in two distinct phases, one part in 1936 and the other in 1943. The 1943 development was built by the Hochtief company as part of an extensive program of subterranean construction in Berlin that began in 1940. The rooms of Hitler were in the newer, lower section and by February 1945 it had high quality furniture taken from the Chancellery along with several framed oil paintings.