Norman – Castle Studies Trust Blog

How Civil Engineering Techniques Can Be Used To Help Inform Cultural Heritage Conservation

Post graduate student Tom Davies explains how he has taken some of the latest civil engineering techniques to help understand the condition of the stone work of old buildings, using Durham Castle as a case study.

Durham Castle was the building of interest for my master’s research project in 2023/4. Durham Castle has an incredible history, being founded in 1072 on the orders of William the Conqueror, to being the seat of the Prince Bishops, to now being part of a UNESCO World Heritage Site and University College for Durham University. The Castle’s rich history and architectural significance makes it preservation crucial, ensuring that its historic features are maintained for future generations.

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My research was based on understanding how a section centred around and above the Norman Chapel, the oldest building in County Durham, behaves under ambient excitation. Every structure experiences ambient excitation under normal operating conditions, it is the study of how a structure moves due to natural stimuli such as how it reacts to windy conditions and how it responds to when people move through the structure. Within the section I investigated, the Norman Chapel was on the ground floor, the Senate Rooms on the first floor, and some of the rooms of the Norman Gallery were on the second floor, with the roof above. These spaces, along with their remarkable examples of Norman architecture, make the conservation of this part of the Castle especially vital. The first non-destructive in situ testing I conducted was ambient vibration testing. This involves using multiple accelerometers in orthogonal directions (at right angles, seen in Figure 2) to record how the structure responds to ambient excitation, in this case measurements were undertaken on a windy day. Every building vibrates naturally at its natural frequency, which is determined by the building materials and structural connections of the building among other conditions. The taller the building, the lower the natural frequency, as they are more flexible. The Castle section I looked at is 3 storeys high, so one would expect a higher natural frequency than that of a structure such as the main tower of Durham Cathedral, which is 66m tall. The recorded accelerations were converted into frequency measurements which revealed information about the natural frequencies. This conversion is important, as when plots are made, it is possible to see different modes of vibration.

In order to characterise the masonry parameters that were used in the numerical model and subsequent simulations, another type of non-destructive in situ test was performed, sonic tests. Some tests were undertaken within the Norman Chapel, as this is the oldest part of the Castle, and its masonry has therefore been subject to the most deterioration of any internal section of the Castle due to its age. Additional tests on a masonry panel in a Gallery (corridor) just outside the Norman Chapel were conducted, this is because this Gallery is a very similar age to the masonry of the rooms above the Norman Chapel, from around the 1600s. From this, the different ages, and therefore state of deterioration, of the masonry within the Castle could be included.

Sonic tests involve hitting the masonry, gently, with an instrumented hammer, shown in Figure 3, and recording the time it took for the subsequent waveform to be registered on an oscilloscope (a machine that shows waves) connected to an accelerometer. Figure 3 shows how this process works, there are two types of waves: P and R waves. The main difference is one travels along the surface of the stone, and the other travels into the stone and reflects off the back of it and returns to the surface. I will focus on the P waves (their names are quite confusing, but it is interesting to know that you can obtain the desired outcome, here the determination of material properties, using either wave). From the recorded wave you can work out the speed of the wave, and using equations you can work out material properties. This is an incredibly important in defining the characteristics of the material within the numerical model. I constructed a finite element model and applied appropriate boundary conditions to represent the foundations of the building, as well as the connections between the section I was investigating and the rest of the Castle. I used the results of the sonic tests mentioned above to determine the masonry material parameters. From the numerical simulations, global frequencies were determined and compared to the results of the ambient vibration testing. global frequency, I mean results that represent the structure as a whole, rather than only a little part of it such as the tower you can see in Figure 4b, or an individual wall. The goal of the finite element model was for its results to be as close to the results of the ambient vibration testing as possible, as this would indicate the model was good at replicating the actual behaviour of the building.

Looking forward, there is a plan to undertake a multi-year project to investigate Durham Castle on a much larger scale, building on the work I have done with the target of investigating the entire Castle. The most intriguing prospect is that when a full finite element model of the entirety of the Castle is built, simulations of different loading conditions can be investigated. This would allow different situations to be modelled and the results determined before any physical changes were done to the Castle.

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Where Power Lies: the archaeology of transforming elite centres in the landscape of medieval England c. AD 800-1200

Between 2018-2021, the Castle Studies Trust awarded Dr Duncan Wright three small grants to research the castle of Laughton-en-le-Morthen. The aim was to develop an innovative new research methodology to understand the near wholesale replacement of existing lords with incoming Norman tenants-in-chief physically showed itself post the Norman Conquest. Here Duncan explains what that has helped lead to.

In October 2021 the Arts and Humanities Research Council (AHRC) awarded Dr Duncan Wright (Newcastle University) an Early Career Research Grant of £200,000 in support of a new archaeological research project.

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Entitled ‘Where Power Lies’, the project will undertake the first systematic examination of the physical evidence for elite centres in the landscape of medieval England between c. 800-1200AD. Many of these high-status places were developed as castles, and the research aims to identify the motivations behind choosing to build a castle at an existing lordly centre, when a site could equally be perpetuated as a manor house or else abandoned altogether.

The success of Duncan’s AHRC bid is partly thanks to the support of the Castle Studies Trust, who funded his research at Laughton en le Morthen (South Yorkshire) with three separate grant awards totalling almost £5000. The work at Laughton, which comprised geophysical and topographic survey, targeted excavation, and the commission of 3D reconstructions, not only helped reveal the complex history of the site but also acted as an important pilot and proof of concept for the new project. Indeed, Where Power Lies hopes to emulate the success of the research at Laughton, and will include some of the same survey techniques, but it will also scale up the focus to look at the national distribution of aristocratic centres with evidence for investment in both church and residential components.

Survey results of geophysical survey of Laughton-en-le-Morthen

After modelling the national picture, the Where Power Lies team will investigate a carefully selected sample of case study sites, which will be subject to topographic, geophysical, and standing building surveys. These investigations will allow us to reconstruct the biography of the case study locations in detail, and to explore how the character and expression of elite power invested in their residential and ecclesiastical complexes evolved over time. Working with the British Museum’s Portable Antiquities Scheme as an official project partner, the research will also produce a new profile of the artefacts of the aristocrats who built and occupied these sites.

By undertaking this work, Where Power lies will shift the focus beyond the relatively small corpus of excavated aristocratic sites of the period which continue to form the basis of our understanding. Instead, by embracing a range of digital technologies and non-intrusive survey methods, the projectwill create valuable new datasets at a number of scales. By generating this new information, the team will demonstrate how the transformation of power centres occurred on the ground, revealing whether castles integrated earlier components into remodelled layouts, or whether they caused greater destruction and a more fundamental schism with the past.

Excavation at Laughton showing remains of a ditch that ran next to a possible entrance way to the Saxon lordly centre.

The team will be led by Duncan as Principal Investigator, who will be accompanied by Professor Oliver Creighton (Exeter University) as Co-Investigator, and a Research Associate who will join the team for the duration of the project. Duncan would like to take this opportunity to thank the Castle Studies Trust for their generous support of his research at Laughton en le Morthen, which strengthened the AHRC bid significantly. He hopes the results of Where Power Lies will prove of interest to everyone associated with the Trust.

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You can read more about the Laughton-en-le-Morthen project here: https://castlestudiestrust.org/blog/2020/08/25/landscapes-of-lordship-searching-for-laughtons-anglo-saxon-elite/

Shrewsbury Castle – more than meets the eye

Shrewsbury Castle Excavation Director, Dr Nigel Baker, reviews the second season of excavations at the castle which has just ended, with an unexpected conclusion.

Shrewsbury Castle has sometimes been described (most often by the writer of this blog!) as one of the best-preserved shire town motte-and-bailey castles in the west of England. This remains true – at least in the sense that it has never been quarried away for gravel, nor had a prison or law courts built on top of it, nor was it demolished and redeveloped after the Civil War. Nevertheless, such a statement now requires a hefty footnote.

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A visitor, walking into the inner bailey at the foot of the motte sees crenelated curtain walls rising from the top of substantial ramparts: the impression of a classic castle sequence with earth-and-timber fortifications renewed in stone, is overwhelming. The 2020 work has however shown that neither the ramparts nor the western curtain walls are quite what they seem. Excavation to a depth of more than two metres in the western rampart has shown that at least half of its height was a product of the post-medieval centuries – with a substantial contribution probably made by Thomas Telford during his ‘restoration’ of the castle in 1786-90, enhanced by his simultaneous lowering of the ground level across the interior.

Shrewsbury Castle excavation trench in western rampartas viewed fromfrom C13 logis block. Courtesy of Nigel Baker

But the medieval strata below Telford’s rubble also show that the western curtain wall, and by implication the standing castle building, the camera regis of the later 1230s, can no longer be seen as simple improvements to the original earthwork castle as the ground beneath them was found to drop away sharply, the slope levelled up by a massive medieval earthmoving operation. It seems that the present outline of the castle – and the familiar view of it from the railway station below, are a product of the early 13^th century (dating subject to confirmation when the pottery has been analysed) – dubbed Shrewsbury Castle 2 by the excavators. The ‘original’ motte-and-bailey, first heard of when it resisted a siege in 1069, must have had a perimeter that was around 25% smaller, confined to the original hilltop. This castle (inevitably ‘Shrewsbury Castle 1’) was nevertheless heavily fortified, as the substantial motte ditch found in 2019 shows. As originally conceived, the ‘inner bailey’ was little more than a lobe-shaped barbican, protecting access up onto the motte, with little room for buildings within it. One of the implications of this is that the most important buildings – like the royal hall – must have been on the motte top.

The medieval landfill operation is also of interest on account of the rubbish contained in its strata. Preliminary visual identification of the animal bones suggests that game species are present, possibly pike, possibly swan, and it is likely that further work on this material will add to the growing corpus of evidence for high-status diet on castle sites throughout the region.

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The excavation was funded by the Castle Studies Trust and supported by University Centre Shrewsbury under Professor Tim Jenkins and Dr Morn Capper. Archaeological direction was by Dr Nigel Baker and Dai Williams and the work was undertaken by local volunteers and UCS postgraduates and undergraduates.

Feature image courtesy of Dr Nigel Baker

Castle Studies Trust Summer Quiz: Name that Castle

With most of us either staying at home or at best having a “staycation” not many of us will have the chance to see castles outside the UK so to whet the appetite for when we can travel again can you name these castles all of which are outside the UK and Ireland?