On 12 June 1943 , they had deliberately ignited a firestorm .
Since May 1940 Allied air raids had killed more than 500,000 civilians , and damaged or destroyed 90 percent of the buildings .
On 12 June 1943 , civilians had deliberately ignited a firestorm .
Since May 1940 Allied air raids had killed more than 500,000 civilians , and damaged or destroyed 90 percent of the buildings .