Contrary to initial guesses, the bomb proved to be a German Luftwaffe SB-1000 ('only' 1000 kg). And de-fusing was quick because the bomb shell was empty. All that evacuation for naught.

So, was it de-fused 63 years ago already, but the shell left there for some stupid reason? Or was this sabotage by some forced-labourers at an armory factory?...

_{*Lunatic*, n.
One whose delusions are out of fashion.}

I was always a bit puzzled by the Alto Adige closings, and now that I think about it I realize that I never read any details about the actual bombs. I wonder whether it might have been a precaution before doing construction work in an area known to have a high risk of containing bombs? I know that the U.S has made available details of each bombing raid (types of bombs, where dropped etc) as well as aerial pictures from which one can get some idea as to which exploded, so it's just possible that they've done the hard work of correlating them, at least for very sensitive areas next to the highway/railway lines.

On a related topic, I once saw, in the Dolomites (Brenta, I think), a warning not to go past a fence because of the risk of mines. Yes, there are still left-over mines from the first world war.