In May 1987, the Golden Gate Bridge was flattened.

The occasion was the 50th anniversary of the graceful span’s opening in 1937. A celebration included closing the lanes to vehicle traffic so people could take a leisurely stroll across. An expert estimated 80,000 would show up.

The real number was 10 times that, with roughly 300,000 souls crammed onto the span itself.

Crowds entered from either end, reports said, creating shoulder-to-shoulder gridlock at the middle that pulled the bridge’s cables alarmingly taut. A voice over a loud speaker repeated over and over, “Get off the bridge. Please, you must get off the bridge.”

Winston Montgomery recalled the scene later in the San Francisco Examiner: “There were cheers as some people started to hurl bicycles over the railing. A stroller tumbled down and sank beneath the waves 220 feet below. ‘Throw the baby, too,’ people yelled, laughing.” As the roadway dropped an estimated 11 feet, Montgomery discussed with his wife “the real possibility that we were about to participate in one of the 20th century’s landmark disasters.”

But there was never any real cause for concern, officials said. Opened three decades after the Great Earthquake of 1906, the Golden Gate Bridge was built to safely flex 15 feet vertically and 27 feet from side to side.

Even so, bridge engineers were intrigued enough by the spectacle on May 24, 1987, to run some quick calculations. Their conclusion: It would have taken three levels of people stacked atop of each other to truly threaten the bridge. Call it a challenge for the centennial.

This article is from the California Sun, a newsletter that delivers must-read stories to your inbox each morning . Sign up here.