The cold squalor of 19th century London was not a beautiful place. As the Industrial Revolution pushed upscale English society into modernity, life for the poor maintained a medieval character. In the neighborhood of Soho, north of central London, asthmatic gray soot thickened the air, the malodorous twang of human feces hung around breathing level, and the water could kill you.

Cholera hit in the summer of 1854. In the first ten days of September alone, more than 500 Soho residents died. By the end of the month, the neighborhood had been almost completely abandoned. It was not the first time the disease would take lives in London, nor would it be the last, but it was certainly the worst. The outbreak has since become known as the birth of modern epidemiology, because of the extensive outbreak mapping from John Snow, an English physician.

Through interviews with Soho locals, Snow was able to record individual cholera deaths by location. On a public map of the area’s streets, he marked each incidence of the disease with a bar. Some neighborhood streets registered only a few deaths, while others displayed staggering results: heavy blocks of black marks, each representative of a human life, stacked ten or fifteen high in certain buildings.

By far the most severe collection of death marks centered around the intersection of Broad Street and Cambridge Street, where a local pump brought water from the Thames River to Soho residents. Snow brought his map to the local council, and the pump was subsequently disabled.

It was later discovered that the neighborhood’s water supply had been extensively contaminated with human excrement. Most homes in Soho had cesspools of night soil– human waste mixed with dirt–sitting beneath their floors. As these pools overflowed, they were dumped en masse into the Thames River. When the water downstream was pumped back to Soho, the residents began a vicious cycle of reconsuming their own waste.