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Costain archaeologists make a once in a lifetime discovery on HS2 project site

HS2 archaeological treasure


14 July 2021


Costain archaeologists working in West London on the HS2 project uncovered a rare set of iron age coins, dating back to the 1st century BC.

The site was undergoing archaeological excavation and following a storm, ground conditions changed revealing where the coins were buried. Analysis led by the HS2’s Costain Skanska joint venture (CS JV) team enabled the significant discovery.

The hoard of over 300 early coins (known as potins) is a significant historical find and was discovered at Hillingdon in August 2020. The find may soon be recognised as “treasure” under British Law.

Describing the moment, the ‘treasure’ was unearthed, Costain’s Emma Tetlow, working as Historic Environment Lead for HS2’s main works contractor Skanska Costain STRABAG joint venture said: “We were coming to the end of our archaeological work on the site when we found a patch of soil that was a very different colour from what it would be expected to be. The patch of soil was dark greeny-blue which suggests oxidized metal, and when we checked more closely, we could see loosely packed metal discs. This is a once in a lifetime find and allowed us to expand our knowledge of what life could have been like in Hillingdon many centuries ago.”

Known as the ‘Hillingdon hoard’, the find dates from the late Iron Age, during a period of change as the Romans began to establish themselves in Britain. The potins are based on coins struck in Marseille, France, about 2,175 years ago. The use of these early coins spread across northern Europe. In England, their use was commonly linked to Kent, Essex or Hertfordshire. The term potin refers to the base metal silver-like alloy used in coins and is typically a mixture of copper, tin and lead.

Because of the significance of the find, and the high number of coins, the local coroner was alerted. The coroner will determine whether the discovery amounts to ‘treasure’ after considering specialist evidence from the British Museum.

The potins were taken to the Birmingham Museum and Art Gallery where they have been cleaned, preserved and sent to a specialist for further analysis where the origins and dating were determined.

The value of the hoard has not yet been determined, nor has its future location. Under the Treasure Act, the Coroner will determine whether the find constitutes ‘treasure’ and if a museum wishes to acquire the potins and recommendations for the find will be made and a potential value placed upon it.

The hoard was found during HS2 works on land that was occupied temporarily. HS2 is not making any claim on the hoard and under the Treasure Act archaeologists are not entitled to a share of any reward.

HS2’s Head of Heritage, Helen Wass said: “At HS2 we are not only building for the future, but we are also preserving the past. This is an exciting find for our team of archaeologists and provides us with more information about how our ancestors lived and settled in London. HS2’s unprecedented archaeological programme has enabled us to tell the stories of from our history and leave a lasting legacy for future generations.”

The archaeological work was agreed in liaison with Historic England to ensure the HS2 site was carefully examined to find, protect or investigate important archaeology before construction begins.

Duncan Wilson, Historic England Chief Executive, said: “They say money talks so what can this unexpected discovery tell us? It takes us back to the tumultuous time of Julius Caesar’s conquest of Gaul. Reaching Britain in 55 and 54 BC he observed the locals using ‘bronze’ coins, an innovation they had adopted not long before through cross-channel migration and trade. Hoards like this are now protected by law so that they can be studied to learn more about how these early coins were used, and perhaps shed light on why they came to be hidden in a seemingly remote place. Extensive projects like HS2 will always bring about archaeological discoveries which is why Historic England works with HS2 to ensure thorough surveys and investigations.”

A similar hoard, the ‘Sunbury hoard’ was discovered in 2010 but the potins were dated much earlier in the Iron Age. Potins from late in the Iron Age, similar to the Hillingdon hoard, have been found previously but in much smaller quantities.

In the London region, the oldest archaeology found by the HS2 team was dated more than 11,000 years old - a period known as the Mesolithic or Middle Stone Age. From this period, stone tools and artefacts were found at locations which suggested people were living on the banks of the river.

Later evidence from the Bronze Age, about 4,000 years ago, such as roundhouses and cremations were also discovered, further indicating human activity near the river. However, until the potins were uncovered there was a large gap in the knowledge gathered from the region with no archaeological evidence of activity for almost 3500 years.

HS2 will not be revealing the exact location where the hoard was discovered at the request of the landowner, who wishes to remain anonymous.