On Sunday August 13 1961, Berliners awoke to find 28 miles of barbed wire coiled across their city, dividing friends and families. Overnight, East German army units had constructed the rudimentary barrier to stem the tide of refugees flowing west. Within days, the first concrete was added, and the city's three million residents knew the Iron Curtain had descended.
In the days that followed, commuters had to find new jobs, and events that had been planned just a few streets away were hastily rearranged. Over the next three decades, 136 people died trying to cross the border. To the rest of the world, the wall appeared impenetrable.
Yet two years after its construction, a chink appeared in the concrete. For 18 days over December 1963 and January 1964, West Berliners were again allowed to visit the East, to celebrate Christmas with their relatives, although East Berliners remained barred from making the crossing. This visa agreement is now largely forgotten, considered by historians as marginalia compared with 28 years of repression. To the 700,000 West Berliners who were reunited with their families after 28 months apart, however, it was hugely significant.
