by LESTER CROSS
When experts 'confirmed' that carbon dating of oak timbers recovered from the bed of the River Teviot showed the wood had been used in the construction of a bridge in around 1350, Historic Environment Scotland rightly hailed the discovery as being of great national importance.
After all, the bridge, close to the Borders village of Ancrum, appeared to date from the war-torn reigns of David II of Scotland and Edward III of England, and carried the so-called King's Way or Via Regia on its route from Edinburgh to Jedburgh.
But now, only four years after the carbon dating test results were produced by the Scottish Universities Environmental Research Centre in East Kilbride with a 1340-1360 construction date, a group of archaeological scientists using a newly developed and much more precise dating method have shown the Ancrum bridge oaks were, in fact, not felled until the winter of 1428/29.
Historians will now need to reassess the role played by the bridge in Scotland's past as it has now been proven the structure was put up in the less turbulent reigns of James I and Henry VI.
The findings from the follow-up research project, carried out by Darren Davies, Danny McCarroll and Neil Loader, from the Department of Geography at Swansea University has been published in great detail by the Journal of Archaeological Science.
The learned paper, produced along with Coralie Mills, explains that the discovery of bridge remains in the River Teviot in 2018 had been described as “one of the most exciting and significant archaeological discoveries in Scotland in recent years” (Historic Environment Scotland, 2020). The site is believed to have been an important, and at times possibly the only crossing point of the Teviot during the medieval period. As such, the bridge would have assumed strategic, ecclesiastical and political importance.
Subsequent investigation and detailed surveys of the site by Ancrum & District Heritage Society and Wessex Archaeology identified that the bridge was constructed using “branders”; a process whereby a wooden frame is positioned in the river with stone or rubble placed upon it. This was the first record of this construction method being applied in Scotland.
"The presence of timber preserved in situ provided an opportunity for dating the structure. During 2019 and 2020, seven oak timber samples were collected for dendrochronological dating", says the report.
According to the team: "The well-constrained felling date range indicated by the radiocarbon dating placed the construction of the bridge during the reign of David II and the Second War of Scottish Independence (AD 1332–1357), a period of significant political turmoil in the region and around the time of the arrival of the Black Death in AD 1350.
"In such turbulent times, even with a tightly modelled age range, the radiocarbon dating results were puzzling and open to a wide range of interpretations regarding who built the bridge and why. A more precise date would enable more targeted historical research."
At the same time as the initial investigations at Ancrum Bridge, a new precision dating technique was being developed called stable isotope dendrochronology. The paper contains a full technical description of how the system works.
"Stable isotope dendrochronology has conclusively shown that timbers with intact bark edge used to construct the sub-structure of the medieval bridge at Ancrum were felled during winter of AD 1428/29. Given that wood was generally worked “in the green” (unseasoned) it is highly likely that the bridge would have been constructed within 12–18 months after felling.
"Significantly, this result shows that the bridge is approximately 80 years younger than the date indicated by radiocarbon dating. The initial objective of this study was to apply stable isotope dendrochronology to refine the wiggle match [radiocarbon dating] date range and provide a felling date that could allow historians to undertake targeted research on the social and political context surrounding construction of the bridge. Somewhat unexpectedly, the stable isotope dendrochronology returned a date well outside the most likely modelled radiocarbon date range".
The Swansea scientists stress that neither the radiocarbon results nor the wiggle matching are errant or necessarily in conflict with the stable isotope dendrochronological dating.
"The wiggle-match determined range 1340–1360 reports only that there is a 95.4 % chance that the date would lie within this range. In other words, there is an approximately one in 20 chance that the true date lies outside of 1340–1360.
"In this case the date for the sample falls outside of the modelled most probable range. In this specific case, using the ‘standard’ probability range resulted in a misinterpretation of the age of the timber samples and therefore the social and political context in which the bridge was built.
"Given the strong isotopic dendrochronological evidence we now know that rather than being constructed during a period of instability and conflict during the reign of David II, the timbers used to construct the bridge at Ancrum were felled during a less turbulent period of King James I’s reign. From this new insight it is now possible to redirect archaeological and archival research to focus on this later period and in doing so develop a better understanding of the role that the bridge played in the social and cultural history of the region."
In conclusion, the study team explain that while their findings will necessitate a revision to the current interpretation of Ancrum Bridge, and an update to the details of its Scheduled Monument designation, "this site remains a discovery of national importance and a rare example of medieval bridge construction methods in Scotland."
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