In September 1870, the Prussian army completely encircled Paris, cutting telegraph lines, blocking roads, and plunging the city into absolute isolation. The invading forces expected the French capital to surrender in silence. Instead, the Parisians looked to the sky. They initiated the first large-scale, sustained airlift in human history using a fleet of giant hot air balloons. The Sky Post chronicles the thrilling and desperate logistics of the Siege of Paris. Factories were converted to stitch massive spheres of varnished silk, launching at night to avoid Prussian artillery. These balloons carried politicians, spies, and millions of letters over enemy lines. But a balloon can only fly one way with the wind. To get messages back into the besieged city, the aeronauts carried thousands of homing pigeons. This book explores the ingenious microphotography developed to shrink thousands of military dispatches onto tiny collodion films, strapped to the legs of birds that braved Prussian snipers and falcons to deliver the mail. Discover a forgotten chapter of military innovation. Learn how a bizarre alliance of hot air and feathers kept the heart of France beating during its darkest hour.