The term 'Open City means different things in different scenarios.

 This is what it meant in 1944... 

On 4 June 1944 Rome was liberated from the German occupation. Rome had been declared an open city which meant that it could be captured without any fighting. This was a welcome relief after the heavily fought campaign at Cassino.

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German POWs with a pet dog in Rome after their  peaceful surrender.
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US Fifth Army Private Elmer Sittion, gets a kiss from an Italian lady on his arrival in the eternal city. Allied soldiers said that seeing the joy on people's faces made them feel proud.

"As the Germans defences south of Rome crumbled and rapidly retreated Rome was declared and open city.

Joyous celebrations commenced when it became clear that the Germans were gone. Despite the fact that Fascist Italy had been one of the key Axis powers, the Allies, especially the Americans, were treated as liberators when they entered Rome. This was in part because of the German occupation. It was also because of the notable affection of the Italian people toward the Americans. Many Italians had either lived in America or had American relatives. The American combat units paused only briefly before continuing north to resume the campaign against the Germans."

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