Cornish tin mine.
Bogged down in history
29 June 2012
Britain was a major source of tin in the ancient world but details of how this important commodity was exploited were sketchy at best - until Andy Meharg and colleagues Kevin Edwards and Ed Schofield got stuck into two West Country peat bogs.
Tin has played an important role in the development of human society. Either on its own or mixed with copper to form bronze, it had a place in everything from coins and jewellery to armour and weapons. But unlike copper, tin deposits are extremely rare, and ancient Mediterranean cultures (from the Bronze Age through to Roman times) had to look to the remote Atlantic fringes of Europe for their closest supplies.
South-west Britain was home to the largest European tin deposits, and this mineral wealth must have been a significant source of economic and cultural contact between Britain and mainland Europe. But there is not much evidence, archaeological or historical, for how the tin trade developed.
Around 440BC, the Greek historian Herodotus wrote about tin sources in the ancient world: 'I cannot speak with certainty, however, about the marginal regions which lie toward the west, in Europe...Nor am I certain of the existence of the Cassiterides Islands, from which we get our tin.' Pytheas of Massalia (modern Marseilles), who is credited with being the first person to circumnavigate Britain around 300BC, also talked of a tin-bearing island named Mictus within six days' sail of Britain.
Cornwall, particularly St Michael's Mount, has long been associated with the 'tin islands' - the Cassiterides - to which Herodotus referred, but it's not much to go on.
Map of tin, lead and copper deposits in the South West.
In an attempt to add to the body of evidence, myself and colleagues at the University of Aberdeen looked to the peat bogs of the south-west. These bogs have been soaking up atmospheric pollution for centuries and we hoped that pollution would include traces of tin released into the atmosphere from mining and tinworking. The sites we chose - Tor Royal on Dartmoor and Dozmary Pool on Bodmin Moor - are themselves better known as the location for Sherlock Holmes' encounter with the Hound of the Baskervilles, and the place where King Arthur deposited Excalibur, respectively. More pertinent to our study, though, is that both lie undisturbed in the middle of an ancient tin-mining region, and both are ombrotrophic - they get all their water from rainfall rather than from springs or streams. This is important because it means any minerals they contain must have been deposited from the atmosphere rather than carried from surrounding rocks or soils.
Our approach was based on the fact that minute particles of tin are released when ore is crushed and smelted, and these eventually fall back to the ground or are washed out of the atmosphere by rain. Assuming these particles had accumulated and lain undisturbed in the bogs, analysing the amount of tin at different depths would give us a sequence of tin exploitation, with greater concentrations representing periods of more intense mining and smelting. And because the bogs are made up of organic material, we could radiocarbon date the layers associated with different phases of tin deposition to find out when they had occurred.
Our specialised equipment enabled us to core 4m down through the peat, so we were able to work out a chronology of tin deposition and, by analogy, of tin mining and smelting, going back thousands of years.
This chronology adds so much detail to what we know about this period that it will allow us to rewrite the story of ancient Britain's trade links with Europe.
Analysis of the Himmelsscheibe, a bronze disk found near Leipzig, Germany, which is inlayed with a gold map of the heavens and dates to around 1600BC, indicates that it contains tin ores from south-west Britain. So British tin was undoubtedly traded to some extent during the Bronze Age, but our findings suggest that production was low.
The cores showed that, at most, there was only sporadic atmospheric deposition of tin into the peat during the Bronze Age, between around 2500 and 800BC, and this pattern continued until early Roman colonisation, around AD100. This confirms what we had already gleaned from archaeological and fragmentary documentary evidence; that there may have been only limited tin mining and bronze production in south-west Britain over this period.
Peat coring at Tor Royal on Dartmoor.
But what of the Roman period? Until now many archaeologists believed the Romans did not exploit British tin until the 3rd century AD, when they had exhausted more accessible Spanish supplies.
Our cores tell a different story. They show sustained and substantial tin exploitation from around AD100 onwards. We don't know if it was the locals or the Romans who were responsible, but as this activity was in the heart of a region considered to have been on the very margins of Roman colonisation, these findings hint that the Romans' economic and social reach in this relatively isolated region was earlier and more extensive than we thought.
Another indication that our miners were part of the Roman economy is that deposition in the peat stops around AD400, when the Romans left, and for the next three centuries the cores show little activity. But then follows perhaps the most remarkable part of our story. Beginning in the 7th century AD the chemical record shows extensive tin-working all the way through to the time of the Norman invasion some four centuries later. This supports what the scant archaeological evidence from this period suggests that Britain was more than likely the only source of European tin by this time, and it was turning up in bronze church bells, pewter, jewellery and armour - most famously on the tinned silver finish of the bronze helmets from the Anglo-Saxon burials at Sutton Hoo in Suffolk.
Our findings imply that tin mining and trading was highly organised in early medieval Britain and, together with finds like Sutton Hoo and the Staffordshire gold hoard discovered in 2009, this suggests that 'Dark Age' society was technologically richer and more organised than many people assume.
As we hoped, coring through the centuries-old, undisturbed peat revealed a unique record of atmospheric pollution deposition from ancient times. Reading these cores in the right way can yield rich information about past human activity where written records are absent or confused, and where archaeological evidence is missing or poor. This can let us address ancient myths and, as here, shed new light on the history of Britain and its place in Europe.
Professor Andy Meharg is Chair of Biogeochemistry at the Institute of Biology and Environmental Science, University of Aberdeen. Email: email@example.com.
Professor Kevin J Edwards and Dr J Edward Schofield are both in the Department of Geography and Environment at the University of Aberdeen.
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