The crews that arrived in Grafenwoehr, Germany, on Thursday were getting ready to work on the construction of a school, NBC News reported.

But at that site — near the Tower Barracks — those workers found a 500-pound, World War II-era bomb.

So explosives experts were called in, Stars and Stripes reported. And while they tried to defuse the device, U.S. Army Garrison Bavaria cleared out.

Well, not the entire U.S. Army base. Some housing and administrative buildings were evacuated after the bomb was discovered, Ray Johnson, garrison spokesman, told Stars and Stripes. NBC News reported that more than 200 people were affected.

“The area is being evacuated so that the bomb can be defused,” Susanne Bratsch, a spokeswoman for U.S. Army Garrison Bavaria, told NBC News. “It will take about an hour to clear the area.”

The base also posted about the bomb on its Facebook page:

Stars and Stripes notes that such discoveries are “not uncommon,” which is true.

Just last month, a 550-pound, World War II-era bomb was found at the stadium of the German soccer team Borussia Dortmund.

Last year, one person was killed when a World War II bomb exploded in Germany, according to reports. Several others were injured in the incident, which occurred at a construction site.

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