125 years old today.

Wikipedia:

The bridge was designed by German-born John Augustus Roebling in Trenton, New Jersey. Roebling had earlier designed and constructed other suspension bridges, such as Roebling's Delaware Aqueduct in Lackawaxen, Pennsylvania, the John A. Roebling Suspension Bridge in Cincinnati, Ohio and the Waco Suspension Bridge in Waco, Texas, that served as the engineering prototypes for the final design. . . .

At the time the bridge was built, the aerodynamics of bridge building had not been worked out. Bridges were not tested in wind tunnels until the 1950s — well after the collapse of the Tacoma Narrows Bridge in 1940. It is therefore fortunate that the open truss structure supporting the deck is by its nature less subject to aerodynamic problems. Roebling designed a bridge and truss system that was six times as strong as he thought it needed to be. Because of this, the Brooklyn Bridge is still standing when many of the bridges built around the same time have vanished into history and been replaced. This is also in spite of the substitution of inferior quality wire in the cabling supplied by the contractor J. Lloyd Haigh — by the time it was discovered, it was too late to replace the cabling that had already been constructed. Roebling determined that the poorer wire would leave the bridge four rather than six times as strong as necessary, so it was eventually allowed to stand, with the addition of 250 cables. Diagonal cables were installed from the towers to the deck, intended to stiffen the bridge. They turned out to be unnecessary, but were kept for their distinctive beauty.