The total length of the Berlin Wall is 91 miles (155 km). It can not only pass through the city centre of Berlin, but also wrap it in West Berlin, completely cutting off other parts of East Germany. In the 28-year history, the wall itself has undergone four major changes. It was originally a barbed wire with concrete columns. A few days later, on August 15, it was quickly replaced by a stronger, more permanent structure. This is made of concrete blocks with a barbed wire at the top. The first two versions of the wall were replaced by the third version in 1965. This version consists of a concrete wall supported by steel beams. The fourth version of the Berlin Wall was built between 1975 and 1980 and is the most complex and thorough. It consists of concrete slabs up to nearly 12 feet (3.6 meters) and 4 feet wide (1.2 meters). It also has a smooth pipe that passes through the top, preventing people from scaling it. When the Berlin Wall collapsed in 1989, there was a 300-foot no man’s land and an additional interior wall. Soldiers patrolling the dog and a sloping ground showed footprints. The East Germans also installed anti-vehicle trenches, electric fences, large lighting systems, 302 watch towers, 20 bunkers, and even minefields. Over the years, the East German government’s propaganda said that the East German people welcomed the wall. In fact, the oppression they suffered and the potential consequences they faced made many people unable to say the opposite. Although most of the borders between East and West contain multiple layers of precautions, there are only a few official openings along the Berlin Wall. These checkpoints are designed to infrequently use officials and other personnel with special permission to transit. The most famous of these is the Checkpoint Charlie, located on the border of Friedrichstrasse East Berlin and West Berlin. The Charlie checkpoint is the main passage for allied personnel and Westerners to cross the border. Shortly after the completion of the Berlin Wall, the Charlie checkpoint became a symbol of the Cold War. In the meantime, it often appears in movies and books. The Berlin Wall did prevent most East Germans from moving to the West, but did not stop everyone. In the history of the Berlin Wall, an estimated 5,000 people passed safely. Some early successful attempts were simple, such as throwing a rope on the Berlin Wall and climbing up. Others are very rash, such as hitting the Berlin Wall with a truck or bus and running for it. However, some others committed suicide because some people jumped from the high-rise windows of the apartment building on the border of the Berlin Wall. In September 1961, the windows of these buildings were opened and the sewers connecting the things were closed. Other buildings were demolished to make room for the so-called Todeslinie, the “death line” or the “death zone”. This open area allows for direct shooting, so East German soldiers can execute Shiessbefehl, a 1960 order, and they will shoot anyone who tries to escape. Twenty-nine people were killed in the first year. As the Berlin Wall became more powerful, the attempt to escape became more elaborate. Some people dig tunnels from the basement of buildings in East Berlin, under the Berlin Wall, and in West Berlin. The other group saved a piece of cloth and made a hot air balloon flying over the wall. Unfortunately, not all escape attempts are successful. Since the East German Guard is allowed to shoot anyone close to the East without any warning, any escaped plot may die. It is estimated that 192 to 239 people died on the Berlin Wall.