How borders are drawn and enforced has far-reaching consequences, whether we live on either side of them or halfway across the world.

In 1987, US president Ronald Reagan famously stood at the Berlin Wall separating the German city—and, symbolically, the world during the Cold War—and spoke to the Soviet Union of peace, prosperity, and liberalization.

“Mr. Gorbachev,” he said, addressing Mikhail Gorbachev, the Soviet leader, “tear down this wall!”

Now Berlin’s mayor has invoked that iconic moment in a message for US president Donald Trump, who has vowed to build an expensive wall to keep out immigrants at the US border with its southern neighbor, Mexico.

“We Berliners know better than most the pain caused when a whole continent is split by barbed wire and walls,” Mayor Michael Müller wrote in German on the city’s website. “Our division destroyed the prospects of millions.”

“Now, in the early years of the 21st century, we cannot let all our historical experience get trashed by the very people to whom we owe much of our freedom: the Americans,” Müller wrote. “I call on the president of the USA not to go down that road to isolation and ostracism. Wherever such divides exist, like in Korea and Cyprus, they cause slavery and pain. I call on the American president: remember your forerunner, Ronald Reagan. Remember his words: ‘Tear down this wall.’ And so I say: ‘Mr. President, don’t build this wall.'”

The whole message, translated, is below: