The device dropped by the Allies over the industrial Ruhr region during the war was found when experts analyzed old aerial photos of the area. It was located at the site of a pump manufacturer in the city’s Hörde district.

"Außergewöhnlicher Bombenfund" bei Wilo in Dortmund-Hörde (derwesten.de) http://t.co/i5dKyfnryU http://pic.twitter.com/zXpisognF4

— 1001portails Deutsch (@1001ptsDE) November 27, 2014

The evacuation was a precaution necessary before the old ordnance could be defused, since the explosive force of such a device is several times more powerful than the force of conventional bombs. The defusing took place around 1200 GMT with some 1,000 experts taking part in the operation.

Old bombs and shells are regularly discovered in Germany, although they rarely are as big as the Dortmund find.

READ MORE: WWII disposal op prompts 45,000 Germans to evacuate (VIDEO)

Two years ago a similar discovery prompted the evacuation of some 45,000 people in the city of Koblenz along the Rhine River. For Dortmund itself it is a fourth such massive discovery since the end of the war.

Around 20 percent of all World War II bombs failed to explode, estimate suggest.

MT @rn_dortmund: bis zu 17.000 Menschen müssen am Sonntag ihre Wohnungen räumen #dobombehttp://t.co/0uTL7YlGLthttp://pic.twitter.com/qthlnGIwB5 ^SV

— Lokalkompass (@lokalkompass_de) November 27, 2014

Darf ich vorstellen, die #dobombe."@Dortmunderisch: Datt wär also datt Mopett http://pic.twitter.com/aotllok0cD"

— David (@daverouge) November 3, 2013

Gespanntes Warten im Medienzentrum auf #dobombehttp://pic.twitter.com/pA0Q28SZ2Y

— Oli Volmerich (@olivol) November 30, 2014

FOTOS Ordnungsamt und Polizei gehen in der Evakuierungszone der #dobombe von Tür zu Tür: http://t.co/vYT3jpMIhA http://pic.twitter.com/WouJmpSxUs

— RN Dortmund (@RN_DORTMUND) November 30, 2014