<Li> Wire mesh fencing: 66.5 km (41.3 mi) </Li> <Li> Anti-vehicle trenches length: 105.5 km (65.6 mi) </Li> <Li> Contact / signal fence length: 127.5 km (79.2 mi) </Li> <Li> Column track width: 7 m (7.7 yd) </Li>

Who built the berlin wall and why did they build it