The question refers to the article of The Man with the Plan. In the article there have been numerous detaila about the Brooklyn bridge that was created by John Augustus Roebling
To explain the hype about the bridge, the story starts with writer’s father disbelieving that the bridge had actually been built. And the family was fully dressed up for the inauguration ceremony of bridge and the narrator said that there was a huge crowd waiting in excitement for bridge opening at the inauguration.
To enhance this realistic recreation of history; following incident is quoted;
“On May 17, 1884, P. T. Barnum led 21 elephants over the Brooklyn Bridge to prove that it was stable”