(CNN)Here's some background information about the Berlin Wall, which enclosed West Berlin from 1961 to 1989, in an attempt to prevent East Germans from fleeing to the West. It became a symbol of East/West relations during the Cold War.
The Wall
The Berlin Wall began as a border of barbed wire fencing and evolved into a fortified concrete barrier with armed East German border guards.
The wall between East and West Berlin was nearly 12 feet high and approximately 27 miles long, with 302 guard towers and 55,000 anti-personnel explosive devices (landmines).
To prevent attempts to scale the wall or escape by digging underneath, the wall was reinforced with barbed wire, spikes, metal gratings, bunkers and vehicles made into obstacles.
A wide-open area of dirt and sand, a buffer zone between the two walls, became known as "no man's land" or the "death strip," where guards in watch towers could shoot anyone trying to escape.
On border grounds, at least 140 people died either by gunshot, by fatal accident while trying to escape, or suicide.
The most famous border crossing was known as Checkpoint Charlie.
Timeline
Photos: The rise and fall of the Berlin Wall
Photos: The rise and fall of the Berlin Wall
West German children interact with East German border guards after the fall of the Berlin Wall in 1989.
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Photos: The rise and fall of the Berlin Wall
East German workers embed broken glass in the top of the Berlin Wall on August 22, 1961, shortly after construction began.
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Photos: The rise and fall of the Berlin Wall
East German border guard Conrad Schumann's August 1961 escape over what was then a simple barbed wire barrier became one of the most memorable images of the Cold War era.
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Photos: The rise and fall of the Berlin Wall
West Berliners wave at relatives in the East, September 1961.
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Photos: The rise and fall of the Berlin Wall
Soviet and American tanks face off at the border crossing known as "Checkpoint Charlie," in October 1961.
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Photos: The rise and fall of the Berlin Wall
East German bricklayer Peter Fechter, 18, is carried away by border guards after being shot and fatally wounded while attempting to flee to the West in August, 1962. Almost 200 people were killed attempting to cross the Wall between 1961 and 1989.
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Photos: The rise and fall of the Berlin Wall
A guard from West Berlin (right) talks to an East Berliner through a hole in the Wall, September 1962.
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Photos: The rise and fall of the Berlin Wall
Martin Luther King Jr. gave sermons in both East and West Berlin during his September 1964 visit to the city. He won the Nobel Peace Prize later the same year.
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Photos: The rise and fall of the Berlin Wall
Checkpoints along the Berlin Wall were temporarily opened in late March and early April 1972, to allow families and friends on both sides of the barrier to reunite over the Easter holidays.
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Photos: The rise and fall of the Berlin Wall
Canadian-American peace activist John Runnings, then aged 68, walked along a section of the Wall in 1986, as a form of non-violent protest.
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Photos: The rise and fall of the Berlin Wall
United States President Ronald Reagan delivers his famous speech in front of the Brandenburg Gate in 1987, urging his Soviet counterpart: "Mr. Gorbachev, tear down this wall!'
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Photos: The rise and fall of the Berlin Wall
Hungarian border guards begin dismantling the "Iron Curtain" in May 1989, opening the country's border with Austria.
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Photos: The rise and fall of the Berlin Wall
East German citizens scale the walls of the West German embassy in Prague in October 1989, in a desperate first step to freedom.
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Protesters carry a banner reading "Gorbi Gorbi help us!" during a visit to East Germany by Mikhail Gorbachev -- then leader of the Soviet Union -- in October 1989.
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Thousands of anti-Communist protesters hit the streets of Leipzig, East Germany, in November 1989. The massive protests were part of the peaceful revolution that helped bring down the Wall.
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Photos: The rise and fall of the Berlin Wall
On November 9, 1989, the East German government opened the country's borders with West Germany. The following day, citizens tried to pull down the Wall with just about any tool they could get their hands on.
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Photos: The rise and fall of the Berlin Wall
People walk on the Berlin Wall in front of the Brandenburg Gate on November 10, 1989.
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Photos: The rise and fall of the Berlin Wall
East German border guards appear in a gap in the Wall after demonstrators pulled down a segment of the barrier, on November 11, 1989.
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Photos: The rise and fall of the Berlin Wall
Thousands of people pass through a checkpoint at Bernauer Strasse, Berlin, on November 12, 1989.
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Photos: The rise and fall of the Berlin Wall
A line of East Germany's famous Trabant cars heads West along a highway near Leipzig, following the fall of the Wall.
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East German border guards peer through the damaged wall, near Checkpoint Charlie, in February 1990.
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People walk along the longest remaining section of the Wall, now known as the East Side Gallery, in August this year.
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Photos: The rise and fall of the Berlin Wall
A graffiti-covered, overgrown segment of the original Berlin Wall, pictured in September 2019.
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February 4-11, 1945 - In the face of Germany's defeat in World War II, the Allies' Yalta Conference agrees to divide Germany into four zones of occupation: Great Britain, France and the United States occupy the western, northwestern and southern portions, and the Soviet Union occupies the eastern. Berlin, located in Soviet territory, is also divided into east and west zones.
1949 - The zones occupied by Britain, France and the United States become West Germany (formally known as the Federal Republic of Germany). The Soviet zone becomes East Germany (formally known as the German Democratic Republic). West Germany is a democratic republic. East Germany is a communist country aligned with the Soviet Union.
1949-1961 - More than 2.7 million East Germans escape to the West. Foreign citizens, West Germans, West Berliners and Allied military personnel are permitted to enter East Berlin, but East Berliners need a special pass to leave.
August 12, 1961 - East German Communist Party leader Walter Ulbricht signs the order for a barricade separating East and West Berlin.
August 13, 1961 - East German security forces chief Erich Honecker orders police and troops to erect a barbed wire fence and began construction of concrete barricades.
August 18, 1961 - US Vice President Lyndon B. Johnson and retired General Lucius Clay fly to Berlin as a show of US support for West Germany.
August 20, 1961 - The US sends a 1,500-troop task force to Berlin as tensions increase along the border.
August 23, 1961 - West Berliners without permits are banned from entering East Berlin.
June 26, 1963 - US President John F. Kennedy speaks to a crowd in West Berlin at the Rathaus Schöneberg (city hall) on Rudolph Wilde Platz: "Today in the world of freedom the proudest boast is 'Ich bin ein Berliner' ('I am a Berliner') all free men, wherever they may live, are citizens of Berlin. And therefore, as a free man, I take pride in the words 'Ich bin ein Berliner.'"
September 12-13, 1964 - Martin Luther King Jr. visits Berlin at the invitation of West Berlin Mayor Willy Brandt. King delivers a sermon on both sides of the wall titled "East and West -- God's Children."
September 3, 1971 - Talks between the US, Britain, France and the Soviet Union lead to the Four-Power Agreement on Berlin, a decree to improve conditions for West Berliners and ease travel to and from West Germany and West Berlin, as well as travel by West Berliners to the East. It also normalizes Berlin's status as a divided city.
December 21, 1972 - West and East Germany sign the Basic Treaty, which normalizes diplomatic relations and recognizes each other's sovereignty.
June 12, 1987 - In a speech at the Brandenburg Gate, US President Ronald Reagan challenges General Secretary of the Communist Party of the Soviet Union Mikhail Gorbachev, leader of the USSR, to "tear down this wall!"
April 1989 - GDR border guards are instructed to stop "using firearms to prevent border violations."
October 18, 1989 - Communist Party chief Honecker is ousted and is replaced by Egon Krenz.
November 2, 1989 - Krenz announces sweeping political and economic reforms.
November 4, 1989 - More than a half million people participate in a pro-freedom rally in East Berlin, demanding free elections.
November 6, 1989 - A preliminary law passes that gives all citizens travel and emigration rights, with restrictions. Travel time is still limited, and authorities can arbitrarily deny permission to travel.
November 7, 1989 - The East German cabinet resigns. Almost half of the members of the Politburo are removed and replaced the next day.
November 9, 1989 - East Germany lifts travel restrictions to the West. Politburo member Guenter Schabowski announces that East German citizens can "leave the country through East German border crossing points," effective immediately.
November 9-10, 1989 - Jubilant crowds tear down the wall piece by piece using their hands, pickaxes, sledgehammers and shovels.
November 10-11, 1989 - Several new crossing points are opened. Tens of thousands of people cross over into West Berlin.
October 3, 1990 - East and West Germany officially become reunified under the name the Federal Republic of Germany.
August 14, 2018 - A Berlin council member announces that a previously unknown section of the wall was recently discovered in a residential section of the city. The wall had been covered by overgrown bushes, which is how it had remained hidden for so long.
