give engineers access for maintenance on the outward-facing side of the barrier. In some places, villages adjoining the border were fenced with wooden board fences (Holzlattenzaun) or concrete barrier walls (Betonsperrmauern) standing around high. Windows in buildings adjoining the border were bricked or boarded up, and buildings deemed too close to the border were pulled down. The barrier walls stood along only a small percentage of the border – of the total length by 1989. Anti-personnel mines were installed along approximately half of the border's length starting in 1966; by the 1980s, some 1.3 million mines of various Soviet-made types had been laid. In addition, from 1970 the outer fence was booby-trapped with around 60,000 SM-70 (Splittermine-70) directional anti-personnel mines. They were activated by tripwires connected to the firing mechanism. This detonated a horn-shaped charge filled with shrapnel that was sprayed in one direction along the line of the fence. The device was potentially lethal to a range of around . The mines were eventually removed by the end of 1984 in the face of international condemnation of the East German government. Border line Until the late 1960s the fortifications were constructed almost up to the actual border line. When the third-generation fortifications were constructed, the fences were moved back from between to as much as . This gave the guards a clear field of fire to target escapees and provided a buffer zone where engineers could work on maintaining the outward face of the fence in East German territory. Access to the outer strip was very tightly controlled, to ensure that the guards themselves would not be tempted to escape. Although often described by Western sources as a "no-man's land", it was in fact wholly East German territory; trespassers could be arrested or shot. The actual line between West and East Germany was located on the far side of the outer strip. It was marked by granite stones (Grenzsteine) with the letters "DDR" carved on the west-facing edge. Around 2,600 distinctive East German concrete "barber pole" (Grenzsäule or Grenzpfähle) markers were installed just behind the border line at intervals of about . A metal East German coat of arms, the Staatsemblem, was fixed to the side of the marker that faced West Germany. On the West German side, there were no fortifications of any kind, nor even any patrol roads in most areas. Warning signs (Grenzschilder) with messages such