The men who dug the foundations came up wrong

The caissons beneath the Brooklyn Bridge towers introduced the world to a crippling illness that medicine had not yet named.

Sealed chambers under the river

Before the first wire was strung, before the towers rose to their gothic peaks, someone had to dig into the floor of the East River and find bedrock. John A. Roebling's design called for two massive stone towers, and each one needed a footing planted deep enough to hold. The solution was the pneumatic caisson — a vast, airtight wooden chamber, open at the bottom, weighted down to the riverbed and pressurised with compressed air so that workers could dig inside it while the river was kept out.

The Brooklyn caisson was lowered into position in 1870. It was the size of a city block and made of yellow pine sheathed in iron, and inside it, men worked by gaslight in air forced to roughly double atmospheric pressure. Soil and rock came up through shafts; the chamber sank a little further with each day's excavation. When the Brooklyn side reached bedrock, about forty-four feet down, work stopped and the caisson was filled with concrete. The New York caisson went deeper — eventually to seventy-eight feet — and the compressed air at that depth was fiercer, the work stranger, the consequences worse.

The name the bridge gave to the illness

Workers coming up from the caissons had begun to report something troubling before anyone understood what was causing it. The pain came on after they climbed out — joint agony, paralysis, collapse. Some died. Some were permanently crippled. The men called it, with black economy, the bends, because of the way victims contorted. Doctors at the time offered no unified explanation.

Washington Roebling, who had taken over as chief engineer after his father's death in 1869, went into the caissons himself — repeatedly, because that was what supervision required. By 1872 he was incapacitated, almost certainly by what we now call decompression sickness: nitrogen bubbles forming in the blood and tissues as pressure drops too fast during ascent. He would spend much of the bridge's remaining construction years directing from a Brooklyn Heights window. Washington's condition was extreme but not unique; the illness disabled or killed dozens of workers on both caissons ↗ before the bridge opened.

The physician who came closest to understanding the mechanism during construction was Andrew H. Smith, the medical officer assigned to the bridge works. Smith documented the symptoms methodically and concluded that rapid decompression was the cause, recommending slower ascent — though the engineering knowledge to act on it fully did not yet exist. His 1873 report is one of the earliest clinical accounts of what would eventually be formalised as decompression sickness. The towers of the Brooklyn Bridge did not cause the disease, but they gave medicine the population of sufferers large enough to begin naming and studying it seriously.

What the towers stand on

The Brooklyn Bridge ↗ opened in May 1883 — thirteen years after the Brooklyn caisson went in. By that point the caissons were long since sealed and forgotten underfoot, their timber chambers entombed in concrete and stone. The towers above them rise to 276 feet, built from Rosendale cement and granite quarried in Maine. They carry four main cables and a deck that, when built, was the longest suspension span in the world.

Walking across it now, the structure that is easiest to see is the least of what was built. The masonry visible above the waterline was comparatively straightforward; it was the work below the river, the months in pressurised darkness, that cost the most. About a hundred and ten workers are estimated to have shown symptoms of the bends during the caisson phase; the exact number who died as a direct result remains uncertain, partly because the connection was not always recognised in time.

The towers have stood for more than 140 years. The men who built their foundations often could not stand at all by the time they finished.