On April 27, 1978, tower number 2 had reached a height of 166 feet (51 m). Just after 10 AM, as the third bucket of concrete was being raised, the cable hoisting the bucket slackened. The crane pulling it up fell toward the inside of the tower. The previous day's concrete started to collapse. Concrete began to unwrap from the top of the tower, first peeling counter-clockwise, then in both directions. A jumble of concrete, wooden forms and metal scaffolding fell into the hollow center of the tower. All fifty-one construction workers on the scaffold fell to their deaths.
I need to look this up, but iI know that it was in one of the larger plazas in the center of the city.
Took this while walking around in Vatican City.