Germans on Saturday marked the 50th anniversary of the rise of the Berlin Wall, which divided Berlin and came to define the Cold War.

The city observed a minute of silence at noon in memory of those who died trying to escape.

Berlin Mayor Klaus Wowereit told a ceremony that the construction of the wall 50 years ago must be a constant reminder to maintain freedom and democracy.

German President Christian Wulff and Chancellor Angela Merkel also attended the ceremony.

After the defeat of Nazi Germany in 1945, the victorious World War Two allies divided Germany into four zones of occupation. The U.S., French and British sectors became West Germany, while the Soviet sector became communist East Germany.

On August 13, 1961, authorities in the communist East ordered all crossing points from East Berlin to West Berlin to be sealed off with barbed wire, later reinforced with concrete. The wall divided streets and neighborhoods and tore apart families and friendships. The wall was designed to keep residents in the east from fleeing to the West. The 161-kilometer wall would later include 45,000 cement blocks and dozens of watchtowers.

Historians say 125 people died trying to cross the wall from communist East Berlin, but some experts have said the death toll is much higher. East German border guards had orders to shoot to kill anyone they spotted trying to escape.

In June of 1987, U.S. President Ronald Reagan delivered a speech in Berlin in which he challenged then-Soviet leader Mikhail Gorbachev to “tear down this wall.”

In November 1989, East German residents brought down the wall and the government in the communist state.

East and West Germany reunited October 3, 1990.