The infrastructure for removing human waste from populated areas — one of the oldest public health technologies, a system whose presence or absence has determined whether cities could grow beyond a few thousand people, and whose massive construction in the 19th century transformed European and American cities from places where epidemics were normal into places where they were exceptional.
The Great Stink of 1858 was the moment London's sewage problem became impossible to ignore. The summer heat caused the Thames — which received the sewage of two million people — to produce a smell so overwhelming that Parliament could not function. Members stuffed curtains with lime chloride and fled. The solution was one of the great engineering achievements of the 19th century: Joseph Bazalgette's sewer system, 1,300 miles of underground brick tunnels intercepting the sewage before it reached the Thames and routing it downstream. The project took sixteen years, cost £6.5 million, and transformed London from one of the most disease-ridden cities in Europe into one of the healthiest. The lesson: the most consequential public health interventions are not medical but engineering. Clean water and safe sewage disposal have saved more lives than any drug or vaccine in history.