A bridge in China made entirely of glass was an engineering marvel – until it cracked.

The Yuntaishan glass bridge in Central China’s Shiniuizhai National Geological Park had become quite the tourist draw when it opened Sept. 20. Aptly named the Haohan Qiao Bridge or Brave Men’s Bridge in English, holidaymakers rushed to cross the 980-foot-long span that sits between two cliffs and rises 600 feet above a canyon.

 But on Oct. 5, something went terribly wrong. Tourists, reporting on Chinese social media, said they heard a crack and everyone rushed to get off the bridge.

“I heard a bang from under…Everybody is screaming. I cried, ‘It’s really cracked! It’s really cracked!’ And pushed the people in front of me to get away,” according to an unidentified tourist, who was quoted in the English language Chinese Daily.

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Staff at the Yuntaishan resort confirmed that the bridge had developed a crack – blamed they said on someone dropping a thermos onto the path - and had been shut down for the time being, according to the newspaper. Tourists were evacuated from the scene soon after the incident and it was unclear if anyone was hurt.

The crack calls into questions a bridge that designers insisted was safe when it was opened.  To dispel concerns about a possible accident, designers played up the fact that the glass was three-quarters of an inch thick – 25 times stronger than ordinary glass - and was treated to be extremely resistant to both bending and shattering. The glass itself is encapsulated by a steel frame.

 “The steel frame used to support and encase the glass bridge is also very strong and densely built, so even if a glass is broken, travelers won’t fall through,” a worker recently told the China News Service.

I guess they didn’t think of someone dropping a thermos on the bridge.