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On a traffic island in the centre of Cornhill, London, near Bank Underground Station in the centre of the city, stands a statue of South African-born civil engineer James Henry Greathead.

Erected in 1994, the statue recognises Greathead’s invention, which made the construction of the London Underground possible and served as the forerunner to modern tunnel-boring machines.

Born in Grahamstown on 6 August 1844, Greathead was the son of a British immigrant who had moved to South Africa in 1820 as part of the 1820 Settlers.

He attended St Andrew’s College in Grahamstown before enrolling at Diocesan College, also known as Bishops, in Cape Town.

In 1859, at the age of 15, Greathead moved to England to complete his education at Westbourne Collegiate School in Westbourne Grove.

After finishing school, he briefly returned to South Africa before moving to London to complete a three-year pupillage under civil engineer Peter Barlow.

In 1863, while Greathead was working under Barlow, the world’s first underground railway opened to the public in London. On its opening day, gas-lit wooden carriages hauled by steam engines carried 38 000 passengers.

Over the next two decades, the underground network continued to expand, with several new lines added.

However, constructing the underground railway network, known as the Metropolitan Railway, proved extremely disruptive to what was then considered the largest city in the world.

This was because of the method used to build the tunnels. Engineers relied on the cut-and-cover technique, which involved digging a large trench, constructing a brick-and-mortar tunnel inside it, and then covering it again.

While the railway helped solve London’s congestion problem, its construction often worsened traffic and disruption at street level.

Meanwhile, Greathead completed his pupillage, worked on several railway projects as a lead engineer, and was eventually put in charge of constructing the Tower Subway beneath the River Thames.

Faced with the engineering challenges of the project, Greathead developed a tunnelling device in 1868 based on an earlier design by Barlow, adapting it for the soft clay beneath London.

The Greathead Shield, as it became known, initially relied on manual labour to bore tunnels through the earth while using a cylindrical shield to prevent dirt collapsing on it.

This allowed tunnels to be built much deeper underground, causing far less disruption at the surface.

The tube-like shape of tunnels built using the Greathead Shield eventually earned the underground railway system the nickname “the Tube”, which remains in use today.

The tunnel constructed for the Tower Subway measured just over two metres in diameter and opened in 1870.

Greathead was later contracted to work on the City and South London Railway, for which he enlarged his boring device to just over three metres in diameter and added high-pressure hoses to extract dirt. The City and South London Railway’s route is now part of the London Underground’s Northern Line.

The line opened to the public on 18 December 1890 and is widely credited as the world’s first electric underground railway.

Greathead was then tasked with constructing the Waterloo and City Railway and the Central London Railway, which would become the next two deep-level underground railways. The Waterloo and City Railway still operates as part of the London Underground and is still known as the Waterloo and City Line. The Central London Railway is also now part of the London Underground, and is also known by its original name, as the Central Line.

However, Greathead never saw the completion of these projects, as he died on 21 October 1896 at the age of 52.

The Greathead Shield continued to help bore tunnels for the London Underground and expand the railway network across the city for the next decade and a half. In fact, the design remained in use until the 1960s with only minor modifications.

Eventually, the manual labour and high-pressure hoses were replaced with rotary cutters, which would excavate ground at the front of the shield and use conveyor belts to extract the dirt from the tunnel.