The Men Who Built The Berlin Wall

"The140-kilometer Berlin Wall was in fact two barriers. The first was constructed rapidly in August 1961. The second, parallel barrier, 100 meters into the Eastern zone, was erected in June 1962.  The area in between the two barriers was known as the Death Strip. The wall was initially constructed as a wire fence. By its demise in1989, it consisted of 45,000 sections of reinforced concrete."

Link