It was 50 years ago that the Soviet-controlled Eastern Bloc began construction of the Berlin Wall. Germany is commemorating the anniversary with solemn ceremonies, including a memorial for those who died trying to climb the wall to escape the Iron Curtain. At noon, Berlin observed a minute of silence in memory of the victims. Buses and trains stopped for the tribute. The Berlin Wall was erected in 1961 on the orders of East German leader Walter Ulbricht to stop a population exodus. At that time, about 2.5 million people had fled East Germany in 12 years. Momentous events in 1989 led to the fall of the wall and the reunification of Germany.