Ive traversed the Manhattan Bridge countless times, but not until I found this explanation in Jed Rubenfelds novel The Interpretation of Murder did I envision how it was constructed. I ll bet youll find it as engrossing, too "The Manhattan Bridge, nearing completion in the summer of 1909, was the last of the three great suspension bridges built across the East River to connect the island of Manhattan with what had been, until 1898, the City of Brooklyn. As the longest single spans in existence, when constructed, were extolled by Scientific American as the greatest engineering feats the world had ever known. Together with the invention of spun-steel cable, one particular technological innovation made tem possible: the ingenious conceit of the pneumatic caisson. The problem to which the caisson responded was this. The massive support towers for the bridge, necessary to hold up the massive suspension cables, had to rest on foundations built underwater, almost a hundred feet beneath the surface. These foundations could not be laid directly on the soft riverbed. Instead, layer upon layer of sand, silt, shale, clay, and boulder had to be dredged, broken, and sometimes dynamited until one reached bedrock. To perform such excavation underwater was universally regarded as impossible- until the idea of the pneumatic caisson was hit upon. The caisson was basically an enormous wooden box. The Manhattan Bridge caisson, on the New York City side, had an area of seventeen thousand square feet. Its walls were made from countless planks of yellow pine lumber, bolted together to a thickness of over twenty feet and caulked with a million barrels of oakum, hot pitch, and varnish. The lower three feet had been reinforced with boiler plate, inside and out. The weight of the whole: over sixty million pounds. A caisson had a ceiling but no man-made floor. Its floor was the riverbed itself. In essence, the pneumatic caisson was the largest diving bell ever built. In 1907, The Manhattan Bridge caisson was sunk to the river bottom, water filling its internal compartments. On land, enormous steam engines were fired up, which, running day and night, pumped air through iron pipes down into the great box. The forced air, building up enormous pressure, drove out all the water through boreholes drilled in the caissons walls. An elevator shaft connected the caisson to a apier. Men would take this elevator down into the caisson, where they could breathe the pumped, compressed air. There they had direct access to the riverbed and hence were able to perform the underwater construction previously considered impossible: hammering the rock, shoveling the mud, dynamiting the boulders, laying the concrete. Debris was discharged through ingeniously devised compartments, called windows, although on could not see through them. Three hundred men could work in the caisson at one time."