Eight decades since German Stukas pounded Belgrade on April 6, 1941

The retaliation followed the coup d'état that overthrew the then Government for signing the Tripartite Pact. The bombing marked the start of the invasion of the then Yugoslavia during World War II.

The number of killed was estimated at 4,000 people, though some sources put it much higher, even up to 17,000.

The Nazis bombed the National Library of Serbia, the only National Library burned to the ground on purpose in WWII.

The air raids led to the surrender of the Yugoslav Royal Army after six days of resistance.

Belgrade was occupied seven days later, on April 13 and was ruled by the Germans until October 1944. The country capitulated on April 17, the Government and the underage King Petar II Karadjordjevic left the country and settled in London.

On Tuesday, Serbia's and Belgrade authorities will mark the 70th anniversary of the April bombing with a series of manifestations.

April 6, 1941, was the first of three bombings of Serbia's capital in the 20th century. The second happened in 1944, this time by the Allies to help push Germans out of the city, and then NATO's campaign in March 1999.

The latter, dubbed The Angel of Mercy, was by far the longest, lasted 78 days and was justified by what the West described as Belgrade's oppression of Kosovo Albanians that might have led to a humanitarian catastrophe in then Serbia's southern province.