In the 1870s and 80s, the construction of the Brooklyn Bridge was one of the engineering landmarks of the day. In order to install the towers firmly on the riverbed, it was necessary to dig through several feet of silt and sewage to the bedrock beneath. This was before the invention of modern dredging equipment, so engineers used a caisson—a room that is sunk to the bottom of the river and then filled with compressed air so that workers can enter it and dig away the river bed manually. 

Working in that caisson must be one of the riskiest jobs ever...