"The East Germans with little cranes were moving huge cement flower pots and positioning them across the roadways that go under the Brandenburg Gate. And so it looked like a joke at first -- they're sealing it off with flowers," MacNeil recounts.
But when he looked to the right and left, he could see the East Germans building barbed-wire fences and later concrete barriers that sometimes incorporated the lower levels of buildings to the distress of some residents.
Hear his account of the East Germans closing the border and the start of the construction of the Berlin Wall:
How would Western powers react? Tensions had been leading up to the wall's construction, and the moment the tangible division between East and West appeared, people wondered if this action would lead to the next world war.
President John F. Kennedy, burned by the Bay of Pigs in Cuba, was reluctant to start a battle over Berlin. He sent U.S. troops from West Germany as a show of force and support but also to serve as a calming force for the angry West Berliners.
In one instance, MacNeil recalls, East German stone masons were adding cinderblocks to the wall as West Berliners jeered them. An East German armored car approached, and the West Germans started pelting it with small paving stones. An American infantry detachment moved in and forced the West Berlin crowd away from the wall.
"I'm not going to start World War Three so some West Berliners can throw stones at the East Germans," the officer in charge told MacNeil.
Hear more of his description of the impact of the wall, and the attempted escapes to West Germany, here:
When the wall came down on Nov. 9, 1989, MacNeil was executive editor and co-anchor of the NewsHour.
"It was one of those moments when you know this is a turning point in history, just as the beginning of the building of the wall in 1961 was a turning point," he said.
He describes the milestone here:
Watch a 1989 NewsHour roundtable conversation about what the fall of the wall meant to Europe and the United States:
-- By Larisa Epatko, Online NewsHour