President John F Kennedy's "Ich bin ein Berliner" speech was a message of solidarity to West Berlin at the height of the Cold War. Some 50 years on, previously unseen photographs of his visit to the city have the power to recreate the drama of the moment.
There's no doubt that Kennedy's speech was one of the great speeches of history.
It's hard to imagine those pressured times now, but 50 years ago the world was divided into two blocs of East and West, each with an arsenal of nuclear rockets pointed at the other.
The atomic battleground would be Europe, and Berlin was its centre.
West Berlin, made up of the city's American, British and French zones, was an island of capitalism in the communist Soviet sector of Germany, also known as the German Democratic Republic.
There was literally a wall round it - the barbed wire and first stages of the Berlin Wall had been erected only 22 months before Kennedy arrived.
And just eight months before the speech, Kennedy had faced down the Soviet leader, Khrushchev, over Soviet missiles in Cuba. There was a real possibility of nuclear war. Fear really was in the air.
Already one person had been shot trying to flee from East to West Berlin. And in recent memory, the East German and Soviet authorities had closed off food supplies to the Western sectors of the city, prompting the air-lift of supplies direct to the city - nearly 5,000 tons a day.
Into these tense and dangerous times stepped the charismatic Kennedy, young for a leader at 46. He spent four days in Germany but it's the visit to the island of West Berlin on 24 June 1963 which captivated the eyes of the world.
And the eyes of a young photographer. Ulrich Mack was commissioned by the magazine Quick to cover the trip. He took 400 photographs on six Leica cameras, each with a different lens, but only six were published, and none on the front page.
Mack told the BBC that the rest had lain in a box in his home until a friend asked where they were. Mack's photographs of the day have now been collated by publishers Hirmer in a book, Kennedy in Berlin, edited by Hans-Michael Koetzle.
Of the day itself, when 400,000 people heard Kennedy utter the immortal line: "Ich bin ein Berliner", Mack remembers little except that it was warm and that he was frantic to get the best picture: "I was crazy about pictures," he says.
He was allocated space on a truck for new-fangled devices called television cameras. It meant that he had a better view than many of the other press photographers and that he was more mobile. The truck moved wherever Kennedy went and Mack moved with them.
End Quote Ulrich Mack Photographer
This was the best work I've ever done”
What strikes you when you talk to Mack these days is how unmoved he was by the historical significance of the occasion.
It was, for him, not a great moment in a history but a great opportunity to take pictures, particularly better pictures than those of his rivals.
Did the photographer ever talk to the president, for example? "Do I get something better if I talk to him? I do not," he replies.
"It was very warm and I was just searching for the best picture.
"I was just one big eye with six Leicas. And this was the best work I've ever done."
The images capture the heightened excitement of what is at times a frenetic scene - the crowds surging to shake hands with the young president. Few worried about security then - it would take Dallas nearly five months later to reveal how imperilled he really was.
The newspapers had reported that Kennedy didn't like Germany - he had fought in the war and was uneasy about the economic progress the loser of that war was making. Spiegel had a headline: "John F Kennedy doesn't like the Germans".
But Berlin changed that. He was greeted by hundreds of thousands of people.
This magnetic leader seemed so different from the dour Konrad Adenauer of Germany or the prim, old-world, patrician Macmillan of Britain or the gracelessness of the brutish Khrushchev.
As the New York Times described it at the time: "Along the route from Tegel airport to the United States mission headquarters in the southwest corner of Berlin, waving, cheering crowds lined every foot of the way.
"The crowds must have nearly equalled the population of the city, but many persons waved once and then sped ahead to greet Mr Kennedy again."
He did not deliver the speech at the Brandenburg Gate, unlike President Reagan in 1987 and President Obama in 2013.The iconic monument which symbolises Berlin was right on the route of the Wall.
Kennedy went there in the back seat of an open-topped limousine, sitting next to Willy Brandt, then the mayor of Berlin and later Chancellor of Germany, and Konrad Adenauer, the incumbent Chancellor.
The Brandenburg Gate itself was just inside East Germany and the authorities had draped its arches with red banners, obscuring the view into the East.
They, too, were alert to a photo-opportunity and they had placed a placard there, pointing West, which listed in English a series of aims: "To uproot German militarism and Nazism; to arrest war criminals and bring them to judgement etc", and then a direct question: "When will these pledges be fulfilled in West Germany and West Berlin, President Kennedy?"
It would have been highly provocative for Kennedy to make his speech there, at the Brandenburg Gate. Instead, he made it on the steps of the town-hall of the Berlin suburb of Schoneberg. Something like 400,000 people gathered in the square as he spoke.
And they erupted at the line which resonated round the world. He had been toying with the phrase for some weeks before. He had discussed it with his main speech writer and with people drafted in to help him with his Boston-drawl German pronunciation, which, it is generally agreed, was pretty poor.
But it was not in the typed transcript of the speech to be delivered - he added it in his own hand. He does seem to have extemporised, going beyond what his advisers had suggested.
Certainly, the Soviet leader Nikita Khrushchev felt he had been provocative.
A few weeks earlier, Kennedy had given a speech which seemed - to Khrushchev, at least - to suggest a more constructive, co-operative relationship between the two great powers. The Soviet leader is reported to have said after the Berlin speech that the two speeches could have been written by two different people.
Did he, by inserting the word "ein" into "Ich bin Berliner" - the normal, conversational way of saying "I am a Berliner" - unintentionally say he was a jam donut?
This claim has often been made, but Berliners of the human variety will tell you that a jam donut in Berlin is not called a Berliner (though it is in the south of the country), so on the day nobody laughed. And anyway, the added word "ein" can be used here to add emphasis.
And anyway, who can doubt the greatness of the speech? Kennedy connected with a people under siege and who had been the survivors of a world war their parents had started and prosecuted to the utmost destruction and defeat.
Berliners loved him. And he cemented the view - in the world and in the Kremlin - that the city was irrevocably part of the West.