A painted line in the middle of a bridge over the Havel River once divided two nuclear superpowers. This deep dive traces how the Glienicke Bridge between Berlin's Wannsee district and Potsdam went from a 1660 wooden crossing for hunting parties, to Karl Friedrich Schinkel's 1834 bascule bridge, to the riveted iron span inaugurated in 1907 after a Prussian design competition, and then into the heart of the Cold War after an artillery shell dropped it into the river in April 1945.

Rebuilt in 1949 and renamed the Bridge of Unity by East Germany, the crossing was closed to West Germans in 1952 and to East Germans in 1961. Because it was the only checkpoint under direct Soviet rather than East German control, it became the stage for the era's most famous prisoner exchanges: Rudolf Abel for U-2 pilot Gary Powers in February 1962, the return of A ...