The Franco-Prussian War began in July 1870, when troops of the North German Confederation invaded France. Prussian troops had effectively surrounded Paris and cut if off from the rest of the world by September 17, 1870.The siege would continue for five months, ending on January 28, 1871, when the French capital fell to the victorious Prussians. During the Siege, a total of 66 balloons carried 102 passengers and 11 tons of mail out of the city and over the German lines to safety. In all, an estimated 2.5 million letters left the city aboard the balloons, along with 400 carrier pigeons. The plan was for the pigeons to carry miniaturized mail back into the city. While mo more than 5 pigeons made it back, the story of the balloons, some of which were built of available dress silk in the city train stations, and the heroic aeronauts who guided them up and out of the city represented one of the few bright spots of the conflict from the French point of view. Following the war, a Paris numismatist produced a set of jetons, or medallions, celebrating each of the successful balloons that left Paris, a complete set of which is on display at the Museum's Udvar-Hazy center in Virginia. Tom D. Crouch, senior Curator of Aeronautics, will offer an "Ask the Expert" talk on these small treasures and the story behind them at 12:30 PM on Thursday September 15. The overlook at the entrance to the Boeing Aviation Hangar at the Steven F. Udvar-Hazy Center. How to attend