The two-and-a-half-year siege caused the greatest destruction and the largest loss of life ever known in a modern city. On Hitler's direct orders the Wehrmacht looted and then destroyed most of the imperial palaces, such as the Catherine Palace, Peterhof Palace, Ropsha, Strelna, Gatchina, and other historic landmarks located outside the city's defensive perimeter, with many art collections transported to Germany. A number of factories, schools, hospitals and other civil infrastructure were destroyed by air raids and long range artillery bombardment.