An Austrian construction worker knew he had struck metal with the shovel of his excavator. But it took police to determine what he had unearthed — nearly 400 live World War II grenades.

The discovery in the Tyrolean city of Innsbruck on Thursday led to the evacuation of apartments closest to the find, while demining experts defused some of the ordnance and blew up the rest. No one was injured.

Police believe the grenades were part of an underground ammunition depot.