The construction of the Brooklyn Bridge began with a freak accident. In late June 1869, John Augustus Roebling, the celebrated designer and builder of wire rope suspension bridges, was surveying his new project site in Lower Manhattan when an approaching ferry crushed his foot against some wooden pilings. Roebling died of tetanus three weeks later, and the job of chief engineer went to his eldest son, Washington Roebling, who had been his father’s right-hand man for construction of the great bridge spanning the Ohio River at Cincinnati, as well as on the design of the new bridge.

Three years later, with construction well underway on what would be the longest suspension bridge in the world at the time, and the first to use steel wires, Washington himself was incapacitated by “caisson disease” (now known as decompression sickness or “the bends”). With the chief engineer confined to his bed in his Brooklyn Heights home, his wife, Emily Warren Roebling, stepped up and steered the completion of one of the 19th century’s most impressive architectural achievements.

When Washington Roebling met Emily Warren at a ball in early 1864—her elder brother, General G.K. Warren, was Washington’s commanding officer during the Civil War—he immediately fell in love. The couple married in January 1865 in her hometown of Cold Spring, New York, and by 1867, when they sailed for Europe together, Emily was pregnant. Their only child, John A. Roebling II, would be born during their trip.

Washington’s father, then at work on designs for the long-awaited East River Bridge project, had sent his son across the Atlantic to research caissons, the immense underwater structures filled with compressed air that were then transforming the construction of suspension bridges from London to Prague.

As preparations for the new bridge project began, Washington and Emily Roebling moved into a house in Brooklyn Heights, just south of where the bridge would be built. Then in the summer of 1869, after John Roebling’s sudden death, Emily’s 32-year-old husband became chief engineer.

Constructing a suspension bridge over the 6,000-foot span of the East River between Brooklyn and Manhattan involved considerable risk. “This was a structure the likes of which had never been made before,” says Erica Wagner, author of Chief Engineer (2017), a biography of Washington Roebling. “Everything about it was unprecedented. Everything about it was radical.”

Workers first scraped away the bedrock, using shovels and dynamite, in order to settle the two gigantic wooden caissons, which weighed in at several tons each. Above water, huge blocks of stone would be hauled up to the top of the bridge towers using iron ropes. The ropes sometimes snapped, resulting in injury and death. Still, according to Wagner, it was the use of caissons that was “by far the most risky and most untried part of building the Brooklyn Bridge”—and the most important.

Far from a desk engineer, Washington Roebling spent as much or more time inside the caissons than his men. In the spring of 1872, he suffered his worst attack yet of what was becoming known as “caisson disease.” At the time, no one knew that coming up too quickly after diving could enable nitrogen to form bubbles in the bloodstream, causing the painful effects of what is now known as “the bends,” or decompression sickness.

“The atmosphere in the caissons was so strange and so awful, the logical rationale then was that the atmosphere [inside] was causing this, not coming out [of the caissons],” Wagner explains.

Washington’s attack of the bends damaged his sight and hearing and left him partially paralyzed. His mind remained sharp, however, and he continued to direct the bridge’s construction from his Brooklyn home, with the crucial help of his wife.

As the historian David McCullough wrote in The Great Bridge, Emily served as both nurse and private secretary, taking over writing all of her husband’s letters and keeping his notebooks. She also reviewed construction plans, visited the site and met with contractors and bridge officials.

As McCullough put it: “She was quite literally his eyes, his legs, his good right arm.” When her independence fueled (false) rumors that Washington had lost his mental capacity, Emily also fought successfully to keep him from being replaced as chief engineer near the end of the bridge’s construction.

For his part, Washington never failed to give credit to his wife for her contributions to the bridge. He wrote later that “I thought I would succumb, but I had a strong tower to lean upon, my wife, a woman of infinite tact and wisest counsel.”

In the end, McCullough wrote, constructing the Brooklyn Bridge would cost some $15 million, more than double John Roebling’s initial estimate, as well as the lives of some 20 men in addition to John himself. The day before its grand opening on May 24, 1883, Emily Roebling earned the honor of driving the first carriage across the completed Brooklyn Bridge.

An article published in the New York Times at the time related an anecdote about Emily’s meeting with contractors bidding to provide the steel and iron work for the bridge: “Their surprise was great when Mrs. Roebling sat down with them, and by her knowledge of engineering helped them out with their patterns and cleared away difficulties that had for weeks been puzzling their brains.”

Emily Roebling’s unconventional achievements were not limited to her role in the Brooklyn Bridge’s construction. In 1899, at the age of 55, she graduated with high honors from the Woman’s Law Class of New York University, and wrote a prize-winning article in the Albany Law Journal arguing for greater equality for women in marriage. But just four years later, she died of stomach cancer at the Roeblings’ home in Trenton, New Jersey.

Wagner resists classifying Emily Roebling as “the first woman field engineer,” as some sources have called her. “To insist that she must have been an engineer is to force her into a paradigm of masculine achievement and categorization. That doesn't recognize the way in which, as a 19th-century woman, she had to work within the confines of her society.”

Engineer or no, Emily’s influence on one of the world’s most famous architectural icons remains undeniable. As Wagner puts it, “I think it's perfectly possible to say that the bridge might well not have been completed without her.”