The Rotterdam Blitz refers to the aerial bombardment of Rotterdam by the German Air Force on 14 May 1940, during the German invasion of the Netherlands in World War II. The objective was to support the German troops fighting in the city, break Dutch resistance and force the Dutch to surrender. Even though negotiations were successful, failing communications on the German side caused the unnecessary bombardment of much of the city centre.
Lights along the fire line memorialize the bombing of Rotterdam, as this picture shows...
More information: http://en.wikipedia.org/wiki/Rotterdam_Blitz