The summer the Thames stank so badly that Parliament built sewers

In the hot June of 1858, the smell of London's river drove MPs out of their committee rooms. Within seven weeks they had passed the law that gave the city the sewers it still uses.

By the 1850s the River Thames was London's sewer. In the first half of the century the city grew from just under one million people to about three million, flushing toilets spread, and old sewers emptied straight into the river, along with the waste of factories and slaughterhouses.

In 1855 the scientist Michael Faraday dropped pieces of white paper into the Thames to see how murky it was, and told The Times that the whole river had become, for the time being, one great sewer.

Most doctors then believed in miasma: that diseases like cholera spread through foul air. London had already lived through three cholera epidemics, in 1831, 1848–49 and 1853–54, which together killed more than 31,000 people. The physician John Snow argued that cholera travelled in drinking water, but few paid attention.

A hot June at Westminster

In June 1858 a long spell of hot, dry weather lowered the river and left raw sewage lying on its banks. The press called it the Great Stink. In the Houses of Parliament, which stand on the river, the curtains were soaked in chloride of lime to keep the smell out. It did not work, and there was talk of moving the business of government to Oxford or St Albans.

Parliament had argued over new sewers and their cost for years. Now it moved fast. On 15 June Benjamin Disraeli brought in a bill that made the Metropolitan Board of Works responsible for the Thames and let it borrow £3 million, repaid by a levy on London households. It became law on 2 August.

a Stygian pool, reeking with ineffable and intolerable horrors

The plan was the board's chief engineer's, Joseph Bazalgette. Instead of letting sewers fall into the river in the middle of town, he built large intercepting sewers that ran alongside it, sloping gently east and catching the old outflows on the way. Pumping stations lifted sewage from low-lying districts into higher sewers, and everything flowed to outfalls well downstream, at Beckton on the north bank and Crossness on the south. Part of the system runs inside new embankments along the river: the Victoria, Albert and Chelsea Embankments.

Work began in 1859 and the system was complete in 1875. It took 318 million bricks.

The twist is that it was built to get rid of a smell, on a wrong theory of disease. It worked anyway. Carrying sewage away from the river Londoners drank from also carried away the cholera. In 1866 the disease struck one last time, killing 5,596 people, and the deaths were concentrated in a part of the East End not yet connected to the new sewers. That outbreak helped convince doctors that cholera spreads through water. It was London's last.

Much of Bazalgette's network still works beneath the city today, in a city about twice the size he planned for.