The staging was powerful: a United States president in front of the Brandenburg Gate at the height of the Cold War, with an East Berlin security post visible behind him.

On this day 30 years ago, President Ronald Reagan stood behind two panes of bulletproof glass 100 yards from the Berlin Wall and called on the Soviet leader Mikhail S. Gorbachev to dismantle it.

“General Secretary Gorbachev,” he said, “if you seek peace, if you seek prosperity for the Soviet Union and Eastern Europe, if you seek liberalization: Come here to this gate! Mr. Gorbachev, open this gate! Mr. Gorbachev, tear down this wall!”

The wall — which had divided the German capital since 1961 — was a physical and metaphorical symbol of the ideological and economic differences that separated the East and the West.