The story of how stone used to build Roman London was pulled out of the ground in and around Maidstone has been revealed to the nation.

Around 36,000 tonnes of Kentish ragstone were quarried, some of it from what is believed to be one of the largest man made holes in Northern Europe, a valley which now stretches from Coxheath to the River Medway near Tovil.

The origins of the stone used to construct the Roman Wall still visible in parts of the City including Tower Hill tube station, have remained a mystery until now.

The mammoth building project, comprising 3.2km of land walls, was undertaken by emperor Septimius Severus in the late 190s AD to protect the thriving city and commercial hub Londinium had become.

Thanks to the painstaking historical detective work of archaeologist Simon Elliott the material, a greenish-grey hard-wearing rock synonymous with the Garden of England, has been traced to riverside areas around the County Town.

Dr Elliott's research and findings and the story of how one of the worlds largest and busiest cities rose from a swamp was broadcast on Channel 5 on Tuesday evening in the first of a new series London: 2000 Years Revealed.

The programme delves into the capital's past, inspired by astounding archaeological finds made during digging to construct tunnels for Crossrail, an ambitious 73-mile railway project connecting London with Berkshire, Buckinghamshire, and Essex.

Through its construction countless artefacts revealing secrets from London's history have been uncovered.

To highlight the true scale of the Romans' building project East Farleigh-based historian Mr Elliott said: "The walls included more than one million squared and well dressed ragstone blocks needed for the facing, an overall ragstone volume of 35,000 cubic metres, requiring 420,000 man days to build and 1,750 voyages of medium sized merchant ships to transport the stone the 127km from the quarries to London."

Dr Elliott has also concluded the quarries, known as metalla, were based in modern day Allington, Boughton Monchelsea, Dean Street in East Farleigh, Quarry Wood near West Farleigh, and Teston.

A dig had already uncovered a Roman Villa in East Farleigh.

"It's fantastic to have been the person to discovered this," he said. "One of the things I love doing is talking to the wider public."

The largest of these metalla by a wide margin was Dean Street which was a staggering 356,400 square metres in volume, making it possibly the largest in the entire Roman Empire.

According to Dr Elliott, only around one fifth of workers in the metalla were skilled - many who came from across the empire - the rest were unskilled labourers largely slaves, convicts, or prisoner of war.

"A lot of them would have been at the bottom of Roman society," he explained. "These were slaves and convicts. A punishment from crimes at the time was to be condemned to work in the metalla but what they often miss out is that it was to work there until death.

"Even for the most basic crimes like robbery people would have been sent to work there.

"If you went into that hole, you weren't coming out."

Sue Robinson, whose home and garden sit in the Dean Street quarry said the discovery was "amazing."

"I've been in touch with Natural England to have it classified as a site of special scientific interest," she said. "There was quite a lot of Roman activity in this part of Kent. It's fascinating."

She joked: "It's been quite difficult digging in the garden because a couple of feet below the ground is the hard ragstone."

While the locations of quarries has changed, the exact same seam is still used today by The Gallagher Group, the company which owns the last tworagstone quarries in Kent at Hermitage Lane, Maidstone and Blaise Farm, West Malling.

Lance Taylor, Chief Executive Officer at Gallagher Group, said: “Kentish ragstone is synonymous with London’s history, having been used on many of the most iconic buildings in the capital, including the Tower of London.

“Today Kentish ragstone is recognised as part of our county’s architectural heritage and is still used in the construction of new buildings throughout Kent, as well as the conservation of many historic ones.

“Gallagher Group continues to invest in the extraction of Kentish ragstone. Thanks to our skilled workforce and ongoing investment in new quarrying and masonry equipment, Hermitage Quarry supplies everything from quarried aggregates to blocks for walling and high-quality finished stone for use in London and across the South East.”

London: 2000 Years Revealed can still be seen on My5 at channel5.com