Nearly half of Koblenz’s 107,000 residents were forced to evacuate on December 4, 2011 as German experts prepared to defuse a World War II-era bomb, the Washington Post is reporting. The 1.8 ton bomb, which was discovered in the Rhine river, lead to one of the biggest evacuations in the country since the war ended.

Authorities set up shelters in several areas of Koblenz, away from the bomb site. Shuttle buses carried approximately 45,000 residents living in a radius of about two kilometers (approximately 1.2 miles) from the bomb site. The residents evacuated because the British bomb would cause massive damage if it exploded. The bomb was discovered a week before the evacuation, alongside a 275-pound U.S. bomb and a smoke grenade, after the Rhine’s water level dropped, due to a lack of rain.

It’s still common for the German government to discover unexploded bombs dropped by the Allies. The bombs usually don’t cause injuries as they’re defused or brought to a controlled explosion. With the Rhine bomb, officials built a dam of hundreds of sand bags in the river bed to pump water out. Koblenz firefighter spokesman Keiko Breitbarth said bomb experts began defusing the bomb after the evacuation.

City officials have said Koblenz they’ve discovered 28 smaller bombs since 1999, as the area was heavily bombarded during World War II. They’re often found during construction work or by farmers plowing their fields.

Written by: Karen Benardello