© Getty Images

Earliest wastewater systems -

One of the earliest examples of a wastewater system can be found at Skara Brae, a stone-built Neolithic settlement in Orkney, Scotland. This primitive design featured "toilets" and drains in each house, and included water used to flush waste into a drain and out to the ocean.

© Getty Images

Earthenware sewage pipe -

The Mesopotamians are credited with introducing clay sewer pipes, around 4000 BCE.

© Getty Images

Nippur -

Evidence of earthenware sewer pipes dating back to this period have been found in the ruins of the Temple of Bel at Nippur, an ancient Sumerian city located in modern-day Iraq.

© Getty Images

Uruk -

Also in Iraq, the ruins of Uruk demonstrate the first examples of brick constructed latrines, from 3200 BCE.

© Getty Images

Hattusa -

Clay pipes, meanwhile, were also laid down by the Hittites, an Anatolian people whose empire centered on the city of Hattusa. Hittite engineers crafted theirs with easily detachable and replaceable segments, crude but effective technical innovations that allowed for cleaning.

© Getty Images

Harappa -

Archaeologists working at Harappa, an archaeological site in Punjab, Pakistan, unearthed evidence of an urban sanitation system, built during the city's final phase of occupation from 2200 to 1900 BCE.

© Getty Images

Mohenjo-daro -

Similarly at Mohenjo-daro, also in modern-day Pakistan, excavations revealed covered drains lining the city's major roads, into which waste water would have been channeled.

© Getty Images

Pyramid of Sahure -

The ancient Egyptians installed an intricate network of copper drainage pipes underneath the Pyramid of Sahure. Later, around 2000 BCE, the ancient Greek civilization of Crete, known as the Minoan civilization, were responsible for constructing sanitation facilities connected to stone sewers that were regularly flushed by rain. 

© Getty Images

Cloaca Maxima -

It was the Romans, however, who built what is regarded as the world's earliest integrated, fully functioning sewage system. Known as Cloaca Maxima, literally "greatest sewer," it was likely completed in 600 BCE, and by the 1st century CE had been enlarged and connected to no less than 11 aqueducts. The outflow spilled into the Tiber River at Forum Boarium.

© Shutterstock

Unusual tourist attraction -

By the 19th century, Cloaca Maxima had became a tourist attraction, the first visitor attraction of its kind.

© Getty Images

Still in use today -

Some parts of Cloaca Maxima are still in use today, testimony indeed to Roman engineering and town planning. In fact, the ancient sewer stands as a highly valued and sacred symbol of Roman culture.

© Shutterstock 

No sanitation -

After the fall of the Roman Empire, there is little record of other sanitation systems in most of Europe until the High Middle Ages. Roads and streets were used as convenient depositories for the contents of chamber pots.

© Getty Images 

The first flush toilet -

In 1596, the first modern flushable toilet was described by English courtier Sir John Harrington. His ingenious device called for a half-meter (2 ft) deep oval bowl waterproofed with pitch, resin, and wax and fed by water from an upstairs cistern.

© Getty Images

The "Great Stink" -

In England, however, and especially in London, most people were used to disposing of their excrement in rivers. But then the "Great Stink" occurred, an event during July and August 1858 in which exceptionally hot weather exacerbated the dreadful stench of untreated human waste and industrial effluent that was present on the banks of the River Thames. The provision of an integrated and fully functioning sewer system for the capital became a government priority.

© Getty Images

Abbey Mills Pumping Station -

Following the Great Stink, Abbey Mills Pumping Station was completed in 1863 to lift sewage from the now expanded London sewer system.

© Shutterstock

London Sewer Week -

Abbey Mills was designed by English civil engineer Sir Joseph Bazalgette and is today worked on by sewer technicians known as "Flushers." The pumping station is occasionally open to the public during London Sewer Week.

© Getty Images

Crossness Pumping Station -

Crossness Pumping Station in the London Borough of Bexley is also open to the public. Described as a masterpiece of Victorian engineering, the building today houses a museum.

© Getty Images

Crossness Pumping Station Museum -

The museum focuses on the Great Stink and the role of Crossness in improving London's sewer system.

© Getty Images

Parisian sewers -

In Paris, tours of the city's sewer system have been popular since late 19th century, and still take place.

© Getty Images

Paris Sewer Museum -

The Paris Sewer Museum chronicles the history of the French capital's sewers. It also details the role of sewer workers and various methods of water treatment.

© Shutterstock

Cologne's sewers -

The sewer system running under Cologne in Germany dates back to the 1st century CE and the Roman Empire. The network was upgraded and expanded in the 19th century with tunnels and channels. Kaiser Wilhelm II was slated to attend the grand opening, and chandeliers were installed in the ceiling to lend the subterranean facility a suitably noble ambiance. In the end the emperor canceled his visit, but one of the chambers, the Chandelier Hall, today hosts music concerts and other cultural events.

© Getty Images

Visiting Cologne's sewers -

Occasional guided tours take place throughout the rest of the sewer complex, a route that takes in the original Roman walls.

© Shutterstock

Prague's sewers -

The sewer network under Prague features some of the most attractive tunnels of their kind found anywhere. The system was built on the orders of Emperor Franz Josef I and were designed more to impress than to get the job done.

© Shutterstock

Visiting Prague's sewers -

Described as a "Bohemian sewer," Prague's subterranean wonder was completed in 1905, building work having started in 1896. Today a visit underground to admire the intricate brickwork is one of the more unusual things to do in the Czech capital.

© Shutterstock

Viennese sewers -

Vienna's sewer system is famous as one of the locations where 'The Third Man' was filmed. The movie, released in 1949, features a scene where Harry Lime (Orson Welles) is chased by police through the sewers' dark and dank chambers.

© Getty Images

The Third Man Tour - Sewer -

Members of the public can join a fascinating tour of this mid-19th century underworld of tunnels and channels, suitably called the "Third Man Tour-Sewer."

© Getty Images

Brussels' sewers -

The Brussels sewers thread their way under the Belgian capital fed by the Senne River. The sewer network first came to use in the 17th century and was expanded 200 years later to measure an impressive 350 km (217 mi) of tunnels, chambers, and channels.

© Shutterstock

Brussels Sewer Museum -

The Brussels Sewer Museum facilitates exploration of the historic chambers as a self-guided tour. The program also includes access to the working sewer tunnels.

© Shutterstock

Barcelona's sewers -

Barcelona's sewer system features vestiges of its Roman past, the drainage channels (pictured) that once serviced Barcino, an ancient Roman colony that stood on the site of the present-day city.

© Getty Images

Visiting Barcelona's sewers -

Besides the drainage channels, visitors can walk the network of 19th-century sewers by joining a guided tour of the system. The best remnants are located below Passeig de Sant Joan, where the old stairs and wall dividers are located.

Sources: (UNESCO) (Britannica) (British Association of Urological Surgeons) (Thames Water) (Visit Brussels) 

See also: What exactly did the past smell like? 

© Getty Images