No single inventor
Sewers were not invented once. Cities in different regions and periods found ways to carry waste and storm water out of built-up areas, and the designs changed as understanding of disease changed. The story has two main chapters: ancient drainage, which was impressive but limited, and the nineteenth-century sewer networks, which were built in response to epidemics.
Early drains in the Indus cities
Some of the oldest known urban drainage comes from the cities of the Indus Valley civilization, such as Mohenjo-daro and Harappa, dated to about the middle of the third millennium BCE. Many houses had bathing areas, and waste water ran through channels into covered brick-lined drains along the streets. Inspection holes allowed the drains to be cleaned. The planning was organized enough that it is widely regarded as a deliberate municipal system.
Drains have also been found at Minoan sites on Crete and at Mesopotamian cities. Their details differ, and it is not always clear how far they handled human waste and how far they only handled rain and washing water.
Rome and the Cloaca Maxima
Rome’s best-known drain is the Cloaca Maxima, “the great drain.” Tradition links its origins to the sixth century BCE and the Etruscan kings, and it began as a channel to drain marshy low ground near the Forum. Over time it was enlarged, vaulted over and connected to other drains. Parts of it are still visible.
It is tempting to picture Rome as having a modern sewer network, but the picture was more mixed. Public latrines and some wealthy homes connected to drains, but many residents used chamber pots, cesspits or public facilities, and waste could be emptied in the street or collected. A constant flow of water from aqueducts helped to flush the drains, a link described in the article on aqueduct engineering. The sewers also emptied into the Tiber, so the waste was moved away, not treated.
The long gap
After the end of the Roman Empire, many of the systems of western Europe fell into disuse. Medieval towns often used cesspits, privies, open gutters and streams. Some cities had local regulations on waste, and some used rivers as drains, with predictable effects on water quality. In places, ditches and covered culverts existed, and drainage works were built, but there was nothing equal to a city-wide network until much later.
Why the nineteenth century changed things
Rapid urban growth during industrialization packed large populations into towns with little drainage. Cesspools overflowed, and waste often seeped into wells or ran into rivers that also served as the source of drinking water.
Cholera outbreaks in the 1830s and 1840s helped draw attention to the problem. At the time, many observers believed that disease was caused by foul air, called miasma, and the response was to remove smells and filth. The British reformer Edwin Chadwick, in a well-known 1842 report on sanitary conditions, argued that improved drainage and water supply would reduce disease. His proposals were influential, though some of his technical ideas were criticized.
In 1854, the physician John Snow traced a cholera outbreak in London’s Soho to a contaminated water pump, supporting the argument that cholera spread through water. Acceptance was gradual, and the broader germ theory only became established in the following decades. It is a good example of the right action, better sanitation, being taken partly for reasons that were later revised.
London’s response
In the summer of 1858, hot weather made the smell from the Thames so bad that it became known as the Great Stink. Parliament acted quickly. The engineer Joseph Bazalgette designed a system of main intercepting sewers that collected waste from older sewers and carried it eastward, to be released into the Thames downstream of the city. The project included pumping stations and was built over roughly the following decade or so. It is usually described as covering more than 80 miles of main sewers, with a much larger network of street sewers feeding it.
The system is often credited with ending cholera epidemics in London, and the connection is plausible, as the city did not suffer large outbreaks after the 1860s. Improved water supply also played a role, so the credit is shared. Releasing raw sewage into the river downstream was a limited solution, and treatment works were added later.
Other cities
Other cities built their own systems. Hamburg began a planned sewer network in the 1840s after a great fire, and Chicago in the 1850s and 1860s famously raised the level of parts of the city to allow drains to work by gravity. Paris, with its tunnels expanded in the nineteenth century, became known for its sewers. Different cities chose combined systems carrying both storm water and sewage, or separate systems for each, a decision with long consequences that cities still deal with today.
From drains to treatment
Moving waste away from people was a major step, but it moved the problem downstream. Treatment through settling, filtration and biological processes developed from the late nineteenth century. Combined with the filtration and chlorination of drinking water, these changes are linked to large declines in waterborne diseases in the countries that adopted them, although exact causes are hard to separate. That history is told in the articles on water treatment and the slow sand filter.
What this history shows
Sewer building was practical engineering long before it was scientific public health. The ancient drains show that the idea was old and could be done well. The nineteenth-century systems show how epidemics and political pressure can turn an old idea into large-scale public works. Sanitation remains a major factor in health worldwide, and in places without safe sewers the same diseases still occur.