A field archaelogist uses a brush on a skeleton in an open coffin during the excavation of a late 18th to mid 19th century cemetery under St James Gardens near Euston train station in London on November 1, 2018 as part of the HS2 high-speed rail project.

Preserve the past: locating and protecting historic sites

Image credit: Getty Images

As engineers and archaeologists excavate sites to pave way for ambitious engineering projects, existing technologies could help protect our ancient history.

A shackled male skeleton discovered in June this year by house builders in a garden in Rutland suggested a gruesome history – rare evidence of slavery in Roman Britain nearly 2,500 years ago. With feet bound by iron fetters, the body seemed to have been thrown in a ditch.

When builders dig, the past pops up - as the hundreds of archaeologists working on the new high-speed rail link HS2 know only too well. The archaeological sector is bolstered by money from road and rail builders obliged to investigate the history of the land they build upon.

As HS2 progresses, the body count is mounting: tens of thousands of bodies famously were disinterred from a burial ground beside London’s Euston Station in 2018 to make way for construction. In 2019, a 19th-century burial ground at HS2’s rail station in Birmingham was dug up and the bodies reburied, but not before archaeologists could examine the skeletons and artefacts buried with them.

Now, archaeologists are exhuming the remains of some 3,000 people buried over centuries in a lost Buckinghamshire church before work on the new link can proceed. While the church, founded in Norman times, was overgrown and almost forgotten, archaeologists knew already of its existence from historic documents. However, they didn’t understand why it was built so far from known dwellings, until excavations revealed it may have once been a private chapel.

Chemistry is just one tool used to reveal secrets beneath the earth, says Jay Carver, lead archaeologist at large infrastructure experts Fusion JV, and it’s useful for revealing bodies. He’s investigating the middle section of HS2, which crosses rural farmland ploughed by oxen and machinery for centuries, an activity that has already destroyed much beneath the surface. Even so, surprises are emerging. Of the 70 or so significant sites investigated on his patch thus far, “at least half of them are completely ‘new’” he says, “and some of them are huge. At a site in Chetwode - now a little hamlet - we’ve discovered a major Roman settlement, evidence of a vast population, thousands of finds. This was a Roman-era market town that was completely unknown.”

Carver’s first move is to look at documentary databases, before using non-invasive tools and finally boots on the ground.

“Human remains always give a very intimate story of someone’s life and death – they are a big part of what we do,” he says. “We found an unfortunate [Iron Age] soul apparently discarded in a ditch with his hands tied behind his back. We’ve found decapitated bodies – a common punishment here during Roman times.”

Using X-ray fluorescence, a technique to work out the elemental composition of materials, a handheld gadget can measure levels of chemical elements in the soil. “Potassium and calcium are a strong indicator of human settlement, while a big reading of lead or copper may show processing activities,” says Carver. “A large reading of calcium on its own may reveal bodies.”

Despite their image as dusty trowel wielders, archaeologists have been using sophisticated high-tech exploration tools for years - from remote-sensing technologies to archives and contemporary aerial and satellite images, through to a host of geophysical tools, which can pick up anomalies beneath the ground without resorting to pickaxes.

These technologies include ground-penetrating radar, which uses high-frequency radio waves to 'see' through roads and concrete to bounce back off buried objects, yielding 3D representations of beneath the subsurface. This was used recently in Pompeii to help spot new areas for excavation. Armed with these insights, archaeologists can avoid damaging different layers of history as they explore.

Magnetometers, which record slight changes in a magnetic field, are also widely used. Long-buried features such as kilns and furnaces have slightly different magnetic properties from the surrounding earth.

However, it’s LiDAR (light detection and ranging technology) – or airborne laser scanning – which has helped reveal digital treasure chests of ancient sites. Typically, drones or planes fly at a constant altitude, equipped with lasers that fire pulses of light towards the ground and receivers measure the time they take to reflect back. It’s an ideal tool to reveal the foundations of historic buildings that nature may have smothered. Data from these aerial surveys are combined with 3D photographs to build 3D maps of the area. These technologies are a boon for large-scale infrastructure projects which are legally obliged to assess the impact of the project on the environment.

Equipped with this level of knowledge and data – the team already knew St Mary’s church existed and what it looked like – big surprises are unlikely, says Carver. “We’re not starting from scratch.”

While a major project to map the UK by aerial photographs is underway, it’s unrealistic to expect the entire country to be laser scanned. “It would be a wonderful idea, but no one can pay for that,” says Carver.

Yet time-saving technologies continue to emerge. Aerial photographs reveal ancient landscapes and throw up patterns that aren’t visible at ground level – yellower crops might reveal buried ruins or roads beneath the surface, where the soil is drier.

Even more secrets can be coaxed from greenery, says Tony Hunt of Yorkshire Aerial Archaeology and Mapping, working with the University of Hull. He’s fitted drones with bespoke near-infrared cameras to measure what rays bounce back from plants, which reflect infrared but absorb other light.

Bespoke algorithms interpret the data and filter causes of differentiation – often with striking results. “We can fly over 50 acres in about 12 minutes,” he says. “We’ve picked up details that geophysical surveys haven’t found.” Most recently, his drones spotted hidden support structures against a hidden Roman wall, part of a known site beneath a park in Malton in Yorkshire. “That caused quite a stir,” he adds.

Conservation and archaeology haven’t always been this hands-off. Stonehenge was once repaired with cranes and concrete. History last clashed spectacularly with development in the UK when one of the few surviving Elizabethan theatres – the Rose Theatre – was stumbled upon by builders in London in 1989, over four centuries after it was founded. Ultimately, the site was preserved thanks to a vigorous public campaign.

In 1970s Dublin, authorities were stunned to discover, as they cleared land for development, one of the richest and best-preserved Viking Age sites in Europe at Wood Quay. “That was an era pre-survey when archaeological finds were a massive shock,” says Carver. “Today, thanks to the [Environmental Impact Assessment] the big-ticket items are already identified.”

That said, new discoveries continue. Work on the A1 in North Yorkshire revealed that Romans had settled there at least a decade before previously thought. Earlier this year, HS2 archaeologists were surprised to unearth one of the best-preserved 16th-century gardens on the outskirts of Birmingham. Highways England’s £1.5bn move to update the A14 in Cambridgeshire has revealed mammoth tusks; rare Roman coins, and evidence of Britain’s oldest beer brewing. As the controversial plan to build a two-mile-long tunnel beside Stonehenge in Wiltshire progresses, some archaeologists are hotly anticipating what excavations will throw up.

Ultimately, it’s cheaper to know about important heritage in advance, says Dr Chloe Duckworth, Newcastle University archaeologist and television presenter. Developers allocate time for investigation, so archaeologists have been surveying HS2 sites for eight years already. “I lived in Nottingham during a time when they just ploughed through gorgeous medieval streets," Duckworth says. “That just doesn’t happen anymore.”

Relations between developers and archaeologists are less fraught than expected, she says: “Developers want an honest assessment of how long something will take, they don’t want the unexpected.”

Today, three-quarters (74 per cent) of archaeologists are employed in the commercial field and developers contribute £218m to archaeology every year. Local authorities spend up to £17m a year on archaeology, but it’s still is a tiny expense for developers – just 0.13 per cent of total construction spending and, as Duckworth notes, it hardly ever causes projects to fail.

While some leading archaeologists see HS2 as a huge opportunity – a giant trench through the country – there is no shortage of colleagues criticising the rail link, accusing it of disturbing ancient landscapes and obliterating history. Chilterns experts say medieval ditch and road layouts will be destroyed. Once historic finds are investigated, they are then covered over. “Some are just too delicate to preserve,” says Carver. “Such as indentations in the ground where medieval timbers have stood.”

Challenges to the profession – and to the armies of hobbyists and volunteers – will come not from industrial diggers but from automation, say some, and projects are underway to explore whether machines can beat the seasoned eye of an experienced archaeologist. Poring over images and data is time-consuming. “Using current methods – assessing databases, geophysical surveys, trial trenching – it can take three years [for HS2] to get a sufficiently accurate picture of what might be on the ground,” says Dr Iris Kramer, founder of grant-winning start-up ArchAI.

An archaeologist-turned-computer scientist at the University of Southampton, Kramer spent weeks on the Isle of Arran, working with maps created by Historic Environment Scotland from a project to laser-scan the entire island – a survey which more than doubled the number of known archaeological sites there.

Kramer has developed an AI to spot telltale signs of ancient, buried sites. This is harder than it sounds – context is everything – and an archaeologist will know whether a circle spotted from above is the trace of a Bronze Age roundhouse or a contemporary feed-bin for cattle. “It takes an awful lot of research to train a computer to do what the human eye can do,” says Carver. “To assess whether these are ancient remains or what’s left from a bunch of greenhouses taken down after the war.”

Kramer is busy developing and using additional data sets from the UK to enable AI to become better at differentiating and spotting historic sites. She believes her tech will offer swift and accurate assessments in early planning stages, saving thousands of hours of desk-based analysis: “It will speed up and de-risk a construction project.”

It hasn’t all been plain sailing: “The biggest bottleneck for any project like this is training data.” Early versions of her technology flagged bomb craters as Bronze Age burial mounds, although this has since been ironed out.

When a site is judged as worth investigating – as was the tiny, ruined Buckinghamshire church – construction projects allow for flexibility. “Archaeology is built into the programme,” says Court.

Now the fate of a 19th-century railway roundhouse recently unearthed near the planned HS2 Birmingham station hangs in the balance. Twin of the Camden Roundhouse – now a famous music venue – it’s thought to be the oldest of its kind in the country and railway enthusiasts are thrilled by the visible surviving detail of the turntable and inspection bays. Whether it will remain on show or is covered for posterity is yet to be decided.

Finds such as these are a publicity bonanza for highly controversial projects such as HS2, which alongside road building have thrown up a horde of treasures from the past. Each site has to pass a threshold of furthering knowledge before it’s investigated. Is the money well spent, asks Hunt, who’s also chair of the Yorkshire arm of the Council for British Archaeology?

“Do we really need to investigate another Iron Age farm when there’s no academic imperative?" he says. "Why not ask developers to donate to archaeology and allow the experts to decide what should be done with it? We could be so much more selective.”

3D technology

Visualise the past

James Morris-Manuel of spatial data company Matterport explains how 3D visualisation technology helps preserve the past

Our platform turns a scan into an immersive 3D digital replica, which uses AI and machine learning to identify objects and provide precise spatial measurements. Using digital twin technology, engineers can virtually visit locations to plan any challenging or potentially invasive construction work remotely.

Movement is a major problem faced in many restoration and construction projects, including HS2 and Crossrail. Traditionally, movement in historic buildings would have been measured by gluing thin strips of glass across cracks and assessing for breaks.

For more accurate analysis of movement, 3D digital twin scans of key areas of historic buildings can be taken via single point, high-powered lasers linked to a central monitoring system which sets off an alarm if sub-millimetre movement is detected. Underneath the surface of the construction site, pipework can also be rigged using this laser system to deliver fast-drying concrete to areas where there’s movement.

3D digital twin technology can also be used in cities, where modernity lives alongside history, and historic monuments must be preserved. When historical features must be removed to enable construction or other works, digital twins capture enough detail for those features to be rebuilt to the same spec after works are completed. 3D digital twins have been used to help restore historic buildings – in Paris, a digital twin is now providing the dataset that is currently being used to help rebuild the Notre Dame Cathedral.

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