Neil Ludlow and Phil Poucher of DAT look at the results of the investigation at Haverfordwest Castle by Dyfed Archaeological Trust (DAT), as part of a major infrastructure scheme embracing the castle and its setting, has revealed what may be part of the medieval town wall, long thought to have been entirely destroyed.
The remains of the castle still dominate views of the town, particularly from the main eastern approach, crowning a steep bluff overlooking the Western Cleddau river. Founded around 1110 by one Tancard, a Flemish colonist, the castle appears to have begun as a partial ringwork and bailey, perhaps adapted from an Iron Age hillfort. Fortification in stone began under Tancard’s grandson Robert FitzRichard, a decade or so either side of 1200, with the erection of a subrectangular donjon; a curtain wall with at least one round mural tower was later added, possibly by the younger Marshal earls of Pembroke between 1219 and 1245. The castle was transformed into a palatial residence with the addition of an integrated suite of apartments of the highest quality, including hall and chamber-block ranges, and a terraced garden enclosure; they are traditionally attributed to Edward I’s queen Eleanor of Castile who received the castle and lordship two years before her death in 1290. The outer ward was also walled in stone, probably during the early fourteenth century. Although it played no part in the second Civil War of 1648, the castle was partially slighted on Cromwell’s orders and was subsequently used as a gaol, which closed in 1878.
Open to the public since 1970, and housing the town’s museum and County Record Office – but still perhaps an under-valued asset – the castle is now the subject of an enhancement programme to improve access, carry out essential repairs and redevelop the museum. The scheme extends to the castle’s setting, with improved landscaping and restoration of the surrounding burgage-plot boundaries. Preliminary archaeological work includes geophysical survey and test-pit recording.
Figure 1: The walling and archway from northeast. The castle donjon is at far left.
Investigating the castle exterior in early 2021, at the summit of the steep bluff, Andy Shobbrook of DAT came upon a stretch of walling that appears to have evaded previous investigations. Now of no great height, but probably truncated, it is pierced by a wide segmental arch of convincingly medieval form (Fig. 1). Although absent from published plans and descriptions of the castle, it is shown on the large-scale 1:500 map of the town produced by the Ordnance Survey in 1889, on which it is labelled ‘Arch’ in the Gothic script reserved for antiquities (Fig. 3). It lies just within the scheduled area of the castle, corresponding with its boundary, and appears to be in a stable condition.
Figure 2: Plan showing the conjectured layout of Haverfordwest in c.1300
The walling may be part of the medieval town wall rather than the castle defences. The town of Haverfordwest, which is notable for its three medieval parish churches – unique in Wales – was founded soon after the castle and by the close of the Middle Ages had become the de facto county town of Pembrokeshire. Defended by an earthen bank and ditch from an early period, probably before 1200, it was walled in stone after the issue of a murage grant in 1264. The defended area was relatively small, immediately next to the castle and always known as the ‘Castleton’ – while the extensive suburb around the extra-mural marketplace to the south received fortified gateways, they were never connected by any solid barrier (Fig. 2). The town wall had largely disappeared by 1700 and, while the gatehouses survived rather longer, the last were removed at the end of the eighteenth century.
Figure 3: An extract of the Ordnance Survey 1:500 map of Haverfordwest, of 1889, showing the castle and walling (labelled ‘Arch’).
Vestiges of the wall were apparently still detectable in 1900 but all traces were thought to have been lost soon afterwards. Stretches of its former line are marked by property boundaries but its entire course is not precisely known, nor the points at which it connected to the castle defences. The walling discovered in 2021 butts against the donjon at the northeast corner of the castle inner ward, and runs northwest for 5 metres before petering out. The remains of a return at its northwest end correspond with a 90° turn shown on the 1889 map, on which it is shown to then run north-eastwards before turning west to continue along the outer edge of the castle’s northern ditch. But the medieval wall must have deviated from this line at some point, to run northwards to the eastern town gate. The arch is 3 metres wide but was probably always too low – and perhaps too wide – to represent an entry. Its function may simply have been to drain the area immediately to the west, which slopes steeply downhill towards the east and seems to have been a continuation of the castle ditch where it ran out at the crest of the bluff (Fig. 3). Two phases of work within the arch are possible, suggesting it was modified and perhaps narrowed at some point.
Dr Sarah Kerr of Trinity College Dublin discusses the ongoing project to look at the impact of climate change on castles with a focus on the ones in West Cork, as they are battered by Atlantic storms.
Over the past two years, two small grants (Research Incentive Scheme, Trinity College Dublin, Ireland; and Higher Education Innovation Fund, UK) has funded research into the impact of climate change on built heritages, and the identification of those most vulnerable, particularly in West Cork, in the south-west of Ireland. Dún an Óir is one such castle at risk, on the edge of Ireland, on the brink of the West Cork cliffs and at the mercy of the increasingly frequent Atlantic storms and high winds.
Dún an Óir is a castle at risk, on the edge of Ireland, on the brink of the West Cork cliffs and at the mercy of the increasingly frequent Atlantic storms and high winds. Dún an Óir is an Irish tower house, a type of stone-built castle, smaller than the sprawling castles built by the Anglo-Normans, such as Trim, County Meath and, indeed, serving a different purpose. The relative small size of tower houses placed their construction within the financial reach of lords, emerging gentry and merchants in both rural and urban areas. Tower house construction commenced on the island of Ireland (Ireland hereafter) in the mid-fourteenth century and flourished in the fifteenth and sixteenth, construction ceasing by 1650. Their abundance led Terry Barry to state that Ireland was ‘the most castellated country in Europe in the late middle ages’ (Barry 2008, 129) or at least ‘one of the most castellated parts’ of the Irish and British Isles (Cairns 1987, 31; O’Connor 1998, 25). If so, then Munster in the south-west of Ireland was a focal point of this activity. The West Cork area in the south-western extent of Munster contains 47-known tower houses, many concentrated along the jagged and island-dotted Atlantic coast. The West Cork tower houses are of particular interest as they are the only castle type remaining in the region; plus, contemporary written evidence allows the majority to be ascribed to a certain clan.
Dún an Óir (Doonanore when anglicised) is located on the island Oileán Chléire (Clear Island), approximately 13km from the Irish mainland. It was built by the O’Driscoll clan in the mid-sixteenth on a coastal promontory (Figure 1). Located on the coast, along with several other known O’Driscoll tower houses, its occupants could oversee the movement of goods through Roaringwater Bay as well as charge passing vessels for anchorage, victualing and exploitation of the waters (Figure1).
This once strategic position is Dún an Óir’s Achilles heel. The building and its immediate landscape are precarious, unconsolidated and unprotected (Figure 1). Exposed on a partially collapsed promontory, its long-term survival is unlikely and our time to understand it short.
Figure 1: Photograph looking north across Roaringwater Bay towards the Atlantic showing Dún an Óir on a rocky promontory.
Dún an Óir comprised four-storeys rising from a rectangular ground-plan. Access was through the south wall, although the east wall faced the neck of the promontory (where it connected to the remainder of the island). Much of the south wall has collapsed yet a garderobe tower remains to the east of the door (Figure 2). Above the doorway a mural staircase (built within the thickness of the wall) can be seen leading to at least the first and second floors. There is a vaulted ceiling between the second and third floors in the form of three pointed arches separated from one another by overlapping slabs.
Figure 2: Dún an Óir tower house, from the southeast, showing the mural staircase extending upwards along the south wall (with thanks to Finola Finlay and Robert Harris for the photograph).
A significant and surviving feature of Dún an Óir is its bawn (curtain wall): a stone wall which in this case abuts the tower house (rather than surrounding it) and stretches west to enclose the remainder of the promontory (Figure 3). Vicky McAlister’s recent book on tower houses indicates that the survival rate of bawns is low compared to the tower houses themselves (McAlister 2019, 22), recalling earlier suggestions that the current 1 in 5 survival rate may be representative of their former inclusion. Dún an Óir is a relatively rare example of preserved ancillary buildings within the bawn. Although they remain only as overgrown footings, there appears to be a kitchen with oven, and two more apparently feature-less buildings that appear to be contemporaneous with the bawn wall (Figure 3).
Figure 3: A simple plan of Dún an Oir tower house, bawn, and ancilliary buildings. The proximity tit he promontory edge is clear.
Dún an Oir’s bawn reaches to the edge of promontory, almost certainly to be further damaged or lost in this lifetime. With this seemingly fixed future, the onus shifts to the researching community in the present to document what we can: this is discussed further in a recent paper on the castle (Kerr 2019). The erosion to the promontory renders further buildings survey, as well as geophysical survey or excavation, no longer safe. Therefore, the next steps of fieldwork may include airborne LiDAR. Greater exploitation of innovative surveying methods may overcome the difficulties posed by the physical landscape and allow the tower house, bawn and ancillary buildings to be understood to a greater depth before the inevitable happens.
Barry, T. 2008. The study of medieval Irish castle: a bibliographic survey. Proceedings of the Royal Irish Academy: Archaeology, Culture, History, Literature 108(C), 115–36.
Cairns, C. 1987. Irish tower houses: a Co. Tipperary case study, Group for the Study of Irish Historic Settlement.
Kerr, S. 2019. Reconnecting Cultural Landscapes: Dún an Óir, West Cork, Ireland, Landscapes, 20:2, 160-177, DOI: 10.1080/14662035.2020.1861725
McAlister, V. 2019. The Irish tower house, Manchester University Press.
O’Conor, K. 1998. The archaeology of medieval rural Settlement in Ireland, Discovery Programme Monographs.
The Castle Studies Trust is delighted to announce the award of six grants, totalling a record £31,000 not only covering a wide geographic area but also a wide range of different types of research:
Caerlaverock new castle with old behind it and the coastline Crown Copyright Historic Environment Scotland
Caerlaverock, Dumfriesshire
The aim is to understand the chronology and geography of extreme weather events in the high medieval period, and the effects they wrought on archaeological features that led to the abandonment of the old castle built in c.1229 in favour of the new built 200m away in c.1277. The latest thinking is that it was a series of extraordinary storm surge events which pushed a series of storm driven gravel ridges across the River Nith.
The methodology to find this out is interdisciplinary, using scientific methods to enhance understanding of archaeological fieldwork. The fieldwork will involve the establishment of a series of transects across the site and surrounding landscape from which cores and samples will be extracted for sediment description, stratigraphic analysis, and Carbon 14 dating.
Depending on Covid restrictions, the aim is to start doing the work in May this year with the receipt of the final data in the autumn.
Greasley_Castle from air copyright Neil Gabriel
Greasley, Nottinghamshire
The production of an interpretative phased floor plan for Greasley Castle in Nottinghamshire. The castle, built in the 1340s, has an obscure history and the understanding of its architectural phasing is at best very cloudy. The site is now a working farm and a number of post-mediaeval structures have been conglomerated around the remains of what is suspected to be a fourteenth century courtyard house with projecting corner towers.
The survey will act as baseline research data for a site which has not previously received serious fieldwork or publication and provide a basis for further research but also for any future conservation needs.
Work on the project will start in the early summer when covid restrictions ease.
Laughton-en-le-Morthen motte and bailey castle and church
Laughton-en-le-Morthen, South Yorkshire
To provide professional illustration and reconstruction which will also be integrated into a co-authored academic article based on the two previous research projects carried out on the site by Dr Duncan Wright and funded by the Trust. A geophysical survey and then small-scale excavation which give a strong indication that the Normans had built a motte on the site of a high-status Saxon dwelling.
Part of the monies will be used to produce phase plans of Laughton during key stages of its development, and a small percentage will pay for a line drawing of the 11th century grave cover incorporated into the fabric of the nearby church. The aim will be to start the work as soon as possible.
Old Wick Tower copyright Historic Environment Scotland
Old Wick, Caithness
Dendrochronological assessment of timber at the Castle of Old Wick, Caithness thought to be one of the earliest stone castles in Scotland dating from the12th century and the period of Scandinavian ascendency. Current thinking though ascribes the date to the 14th century. Analysing these samples will hopefully provide an answer.
With no architectural features or physical “independent” evidence analysing the remains of a timber joist-end (in poor condition) in one of the joist ends remains the best chance of being able to find an answer.
The taking of the samples is likely to take place in September when conditions are still going to be favourable as the castle is situated next to the North Sea and the sample can only be found 8 metres above ground level.
Richmond Castle copyright English Heritage
Richmond, North Yorkshire
Co-funding a three-week excavation of Richmond Castle, one of the best preserved and least understood Norman castles in the UK. The aim is to understand better the remains of buildings and structures primarily along the eastern side of the bailey including near the 11th century Robin Hood tower and near Scolland’s Hall.
Subject to the scheduled monument consent being granted the excavation will take place in late July.
Warkworth Castle, copyright William Wyeth
Warkworth, Northumberland
Geophysical survey to explore evidence for subsurface features in and around the field called St John’s Close in a field adjacent to the castle with the aim to establish the location and eastern extent of the castle’s deer park in the 16th century as well as its entrance way. It also hoped to find evidence of a routeway running parallel to the possible park boundary which could represent an early route to the castle’s gatehouse from the south-west.
The plan is to do complete the geophysical survey by the end of March.
To keep up to date with how these projects progress over the coming months you can:
Lead Archaeologist on the Druminnor Castle excavation, Dr Colin Shepherd, looks at the results of the ground penetrating radar (GPR) survey of the castle in funded by the Castle Studies Trust in 2019 and what that means for future work at the site.
As a consequence of the GPR geophysics, that were generously funded by the Castle Studies Trust, we have a number of new and potentially interesting anomalies to be investigated. Furthermore, the GPR research has also been instrumental in clarifying other aspects of previously excavated evidence. This has been made possible as, contrary to most instances, the geophysics at Druminnor have been incorporated into the ongoing investigation rather than simply as a precursor to excavation.
The GPR generated 286 ‘radargrams’ or sections across the site and much time and effort has gone into analyzing these. The radargrams were compared to actual excavated sections. This permitted the creation of a ‘key’ that has allowed us to extrapolate from the excavated sections to unexcavated parts of the site. As a result, we can, fairly comfortably, suggest a developmental plan of Druminnor spanning the 13th to 18th centuries (Figure 1).
Suggested phasing of Druminnor Castle by Colin Shepherd
The GPR has suggested the extent of a hardcore platform that appears to have supported the ‘Old Tower’. This was thought to have been the earliest part of the castle but without hard evidence. We hope to test the presumed limit of this platform as we extend our trench southwards from the well that sat within the tower. (As you will recall, the GPR alerted us to that remarkable feature that became a focus for our 2019 season.) The GPR suggests that there may be a revetment supporting the platform at that point. Also, any relationship between this platform and the mid 12th-century kiln will be important in attempting to date that platform and, by extension, the Old Tower itself.
Well found in tower as a result of the GPR survey
The radargrams have also demonstrated the probable line of a terrace and sunken formal garden (red hachures on plan) and permits the excavated section of revetment and steps (shown in black) to be placed in its proper context. This garden probably dates to the 16th or 17th century, though exactly when is still debatable. The construction of the terrace removed all trace of the earlier (early to mid 15th century) ditch and so must post-date that. A late 17th-century Dutch pipe bowl found in the fill of a post hole associated with the steps suggests its removal at around that time or shortly thereafter. No trace of the terrace appears on the estate plans of c.1770.
The line of the defensive ditch has been shown by the radargrams to extend westwards from the excavated portion in Trench 11. This gives us an accurate alignment permitting its course to be drawn, even though the middle section was removed by the terrace. Where its return is at the western end of the site is still a mystery. The eastern arm was excavated in Trench 2 lying beneath the later (early 16th-century) lower courtyard. The 15th-century upper courtyard incorporated the tower with the surviving hall block (shown in blue). The courtyard’s west range can be estimated from remains found during the kiln excavation, but its eastern boundary was removed when the lower courtyard was added.
Finally, the GPR revealed the line of the outer enclosure wall as depicted on the estate plans. This was sampled in 2019 and the base of the wall found. The date of this feature is presently unknown and further work needs to be done to try to clarify that matter.
Evidence of landscaping material in outer enclosure copyright Iain Ralston
Sadly, work planned for 2020 included the extension of the ‘well trench’ in the car park to look for the possible revetment suggested by the GPR as well as opening a much bigger area across the outer enclosure wall, as located by GPR. This sits beneath a good metre and a half of later landscaping material (see picture, courtesy of Iain Ralston) and, for safety and archaeological reasons, demands a much larger trench. The keyhole sample trench indicates good survival and, it is hoped, evidence will be found to date the feature and to help explain when this became the northern boundary of the castle enclosure.
The excavated evidence together with the GPR results permit this developmental plan to be made and rough dates affixed. It is worth noting that, prior to our investigations, Druminnor was believed to have consisted solely of the surviving hall block with an attached tower at its western end. Everything not in blue on the plan, therefore, was formerly completely unknown.
Access in 2021 is still, sadly, in the laps of the Gods owing to Covid, but it is hoped that we will be able to get back on track later this year to look for more goodies!
Dr Rowena Banerjea, University of Reading, UK, with funding from a British Academy/Leverhulme Small Research Grant talks about the research project she works on All Along the Watchtowers! https://research.reading.ac.uk/castle-geoarchaeology-heritage/
The buried or below-ground archaeology at castle sites can be exceptionally well preserved because of its burial under masonry. However, it is often overlooked in conservation and management plans in favour of protection and consolidation of standing remains and developments such as reconstruction and rebuilding projects. It provides an important lens through which we can examine important phases and hiatuses in the developmental history of these monuments.
INSERT FIGURE 1. Well-preserved stratigraphy at Château de Gien, France, from c. 9th – 11th AD occupation, sealed below later masonry and collapse.The rectangles show where micromorphology samples were collected, and the circles mark the locations of spot samples for other scientific analyses. Photo credit Quentin Borderie.]
This project has been made possible due to its project partners and collaborations with several other research projects. The castle case studies represent a diverse range of cultural, environmental and heritage contexts across Europe, in which we could examine the preservation of stratigraphy, biological remains, artefacts and materials:
Castle Keverberg (Kessel), the Netherlands, which consisted of an original stone tower built in 1100 and covered by a motte-and-bailey castle;
Several French castles, which are Château de Caen, built in 1060, Château de Gien, which today hosts the National Museum of Hunting with the remains of an early (c. 9th – 11th AD) Carolingian castra below, Château de Loches and Château de Boves;
Two Italian case studies, Castelseprio, a UNESCO World Heritage site, and Montegrotto;
Dunyvaig Castle, Islay, Scotland, formerly the naval fortress of the Lords of the Isles, the chiefs of the Clan MacDonald.
This project developed a framework for geoarchaeological research at European castles to target archaeologists, castle curators and heritage management policy-makers, so that our guidance can influence their future excavation strategies and conservation plans. Geoarchaeology applies environmental science techniques to archaeological research questions. Soil micromorphology is a geoarchaeological technique that enables us to conduct a micro-excavation by analysing a slide, or ‘thin section’, produced from an intact, small block collected from the archaeological stratigraphy, so the inclusions are still in situ. The slide is analysed using a geological polarising microscope. Under the microscope, we record the same soil properties as archaeologists do in the field and additional ones, to understand the processes by which materials were deposited, how they have decayed due to chemical weathering, and how later human and faunal disturbances have affected the stratigraphy.
FIGURE 2. Micromorphology sampling of turf modifications to the curtain wall at Dunyvaig Castle, Islay, Scotland. Photo credit The Dunyvaig ProjectFIGURE 3. Micromorphology sampling of occupation deposits sealed below later masonry and collapse during excavations ahead of conservation work on the eastern range of Cēsis Castle, Latvia. Photo credit Alex BrownFIGURE 4. Micromorphologyor ‘thin sections’ from Elbląg (Poland) and Karksi (Estonia) castles. Photo credit Magnus Elandner
Soils and sediments are the backbone of the archaeological record. Our data revealed important stories within the soils about the early development of castle sites, the activities that took place inside different areas of the castle and how they may relate to the activities in a castle’s hinterland. We noticed that the preservation of the stratigraphy was exceptional owing to its burial under later masonry structures, masonry collapse and successive occupation layers; a phenomenon which is also observed on urban sites and Near Eastern tell sites.
Our results highlight the great potential and requirement for scientific analysis of these deposits when they are uncovered by excavation and/or building activities. These building activities include the conservation and renovation of the standing architecture and the removal of rubble, which can unseal buried archaeology affecting its preservation. Our analyses have revealed microscopic evidence for in situ animal husbandry and horse stabling, as well as the types of fodder that livestock were fed, crop processing activities, and periods of soil formation where areas of a castle have been abandoned or changed use. For example, at Castillo de Molina de Aragón, Spain, microstratigraphic data show the changing nature of the occupation the citadel, from the Islamic to Christian period which could possibly indicate a change in its role from a clean, well-maintained space to one where livestock roamed. The Islamic plaster floor surface was kept clean and very little domestic refuse accumulated ̶ a soil formed over it, followed by a substantial destruction horizon. In comparison, units of discarded material and trampled floor surfaces characterise the (Re)Conquest phase, c. 1154, and a series of plaster floor surfaces with associated occupation residues containing herbivore dung showing that livestock were present, which probably relate to modifications during the thirteenth and fourteenth centuries.
Steven Spencer and Elena Faraoni of the Hoghton Tower Preservation Trust, look at the results of their work, funded by the Castle Studies Trust in 2019, in trying to find out more about Hoghton Tower in Lancashire.
Hoghton Tower sits 650 ft above sea-level in the heart of the Lancashire countryside. The stories of its visitors and family members are documented and shared whether it be in books, portraits, family albums or documents in the Lancashire archives. But there is one story which has always intrigued us and that is: what was the first tower of Hoghton Tower and where was it? It is clear when looking at the building today that this, like many other historic houses, is a ‘patchwork’ of different projects by different generations interlaced and blended…but where did Hoghton Tower start? Where was the original tower?
There are some clues: the ageing of the stone, the position of the well house, family stories passed down the generations, the shape of the windows and a mysterious mound of stones on the north side of the buildings. One of these stones has an intriguing mason’s mark… Spurred on by the interest of a group of our amazing volunteers who had just finished some research into historic graffiti and masons’ marks it was time to do some investigation under the guidance of Dr Mike Nevell and his team at Salford University. We designed a research project based on archaeological digs, building recording, geophysics and archives research based on the key exam question “where was the great keep of the Hoghton Tower hill?”
North side of Hoghton Tower (copyright Hoghton Preservation Trust)
Thanks to the grant from the Castle Studies Trust, work quickly got underway. Through a series of Salford-led workshops, the team surveyed, recorded and reviewed old photographs and pictures.
Then there was the wonderful five-day archaeological dig.
As they passed through the perimeter fencing on to the dig site, the usually mild-mannered volunteers underwent personality transformations as pairs of friends and even married couples were ‘pitted’ against one another. Was this the site of a 14th century Pele Tower, a 1643 victim of the First Civil War, who would make the crucial find?
Under the patient guidance and control of the Salford team, the test pits were marked out and the excavations began, to many this was the chance of a lifetime and was eagerly embraced. Each find was announced with enthusiastic shouting from the discoverer and muted derision from those yet to make a meaningful contribution.
Hoghton Tower Gatehouse from inside the courtyard (copyright Hoghton Tower Preservation Trust)
As the week progressed, 14th to 19th century finds were unearthed, thankfully shared out between the eight test pits. Clay pipe bowls (1640 to 1680), a musket ball, heat affected glass, sherds of medieval pottery and fragments of medieval roof tiles. Below a stone rubble layer, evidence of a stone-built structure was revealed in the form of large dressed stone blocks, together with walls and a stone flagged floor.
Spurred on by the whole experience, and encouraged by the de Hoghton family, the volunteers have produced and presented an ‘Outdoor History’ tour which aims to share the latest thoughts and discoveries.
Was this the site of the Hoghton Tower? Did we find anything categorical? Well yes and no. The archaeology revealed previously unrecorded stone structures. These together with the artefactual evidence were able to confirm that this part of the hilltop was occupied during the late medieval/early post-medieval periods. The geophysics also gave us other areas that warrant more digging and researching. So, some confirmation but also a lot more to understand and discover on this windswept hill!
Hello! A personal introduction before we get down to the geophysics. I’m Kayt Armstrong, and I am an advisor to the Castle Studies Trust as a specialist in the use of geophysics in archaeology. I am also a member of the board of the International Society for Archaeological Prospection, and I represent the UK on a European research network about soils and geophysics in archaeology. I obtained my PhD in Archaeological Geophysics from Bournemouth University in 2010. I have worked in the UK and Europe (Greece and Italy) since that time, conducting archaeological geophysics in a variety of research and developer-led contexts. I help the CST evaluate funding applications that have geophysical elements, and also comment on the reports from any resulting work.
If you were a Time Team enthusiast, you probably already know the answer to this one!
Geophysics is the study of the physical properties of the earth (or other planets – you can do astrogeophysics!). It is an extensive term that encompasses whole planets, right down to understanding the microstructures of stone. Archaeological geophysics falls into ‘near-surface geophysics’, which studies the first 30m or so of the ground. In fact, commonly, archaeological geophysics is only really concerned with the top 2m or so; material in the topsoil, rather than the bedrock.
Geophysicists use a variety of methods and instruments to get information about the physical properties of the ground, such as its ability to conduct electricity, or its magnetic properties. Small variations in those properties can then be mapped. Buried archaeological material causes variations in the properties in predictable ways. This means we can map buried archaeology using these methods, without having to dig everything up.
When it comes to Castles, there are three main geophysical methods: earth resistance (‘resistivity’), magnetometry, and ground-penetrating radar (GPR). All three techniques look at slightly different aspects of the sub-surface, and all three have benefits and weaknesses. It is really best to combine methods to get as complete a picture as possible, as they will all tell you slightly different things.
Magnetometry
Magnetometry is probably the most commonly used technique in archaeology. It uses sensors to look at small variations in the strength of the earth’s magnetic field, to look for changes caused by buried material. The soil on sites where humans live becomes more magnetic over time, due to things like fires for cooking and warmth and the fermentation of waste material. This material becomes the fills of cut features like pits and ditches. These end up more magnetic than the soil they are cut into.
Structures used for processes involving heating, such as kilns, furnaces and ovens, become even more strongly magnetised and have a very characteristic appearance in the data. Similarly, fired ceramic building materials like brick or tile have a distinctive signal, as do igneous or metamorphic rocks (those modified by heating during their formation).
Magnetometry survey of Pembroke, funded by the CST in 2016
Magnetometry is very fast, covering upwards of 10ha a day if using the latest equipment. It is also relatively easy for community groups to employ. However, the pace will be somewhat slower using hand-carried single sensors. The plus-sides are the speed of survey and the wide variety of archaeological features that can be detected and mapped. The downsides are that this method is strongly disrupted by ferrous material in the survey environment, and has problems on igneous and metamorphic geologies as happened with the survey of Tibbers in 2014. It is also not very useful for mapping stone remains that are not strongly magnetic (such as some sandstones and most limestones). Modern infrastructure within or adjacent to the survey area has a far greater impact on the results than any buried archaeology (as happened in the Wressle survey of 2019), masking it from detection. It is practically not possible to use this method in urban areas. This method cannot detect smaller structures if they are buried more than about 2m below the ground surface. Features in the first 2m can usually be detected but the size of the anomalies that can be distinguished depends on the resolution of the readings taken. However, this method doesn’t let you understand the depths of the anomalies, and so isn’t as helpful on multi-period sites.
Earth Resistance
Earth resistance examines how easy it is to pass an electrical current through the ground. The resistivity of the subsurface varies in relation to several properties. Still, the most substantial effect is caused by variations in moisture content. The fills of cut features like pits and ditches (as witnessed in the 2018 survey at Laughton which showed a possible ditch, confirmed in the 2019 excavation and of Tibbers which lead to the discovery of a new inner bailey) tend to have a more open texture than natural soil. They usually also contain more organic matter. This means they are generally wetter than the ground they are dug into. Conversely, buried structures like walls and floors, are usually much drier than the material surrounding them, because they can’t absorb as much water.
Earth Resistence Survey at Tibbers, co-funded funded by the CST in 2016. Copyright HES
This technique can be applied in two ways. You can collect a grid of readings over a flat area to examine the first 2m or so, producing a plan view. You can also collect long lines of readings with increasingly wide measurement points. This is called ‘Electrical Resistance Tomography’ or ERT, and produces vertical pseudo-sections through the ground, and can reach greater depths, typically in archaeology 8-10m.
The plan-view method typically involves 2 probes on a mobile frame, and two remote probes connected by a cable. 2 of the probes inject a current, and two measure the resistance to it. It is especially useful for mapping buried stone structures. It is therefore handy on ‘Castle’ sites where multiple building phases can be expected. It is relatively slow, however, and relies on being able to insert probes into the ground to get the readings. This is fine on a lawn or field, and it can work on paths and gravel, but the results get very noisy, and it isn’t possible over flagstones or tarmac or concrete. You also need to be able to manoeuvre the cables and place the remote probes at an appropriate distance. This method also doesn’t let you understand the relative depths of various anomalies.
ERT is less commonly used in archaeology, but it has some specific applications in the study of large defended sites. Because it can resolve structures at a greater depth than the plan-mode, it can be used to examine the construction of large structures. This includes moats, earthen banks and buried fortification walls, and other such features. If multiple adjacent profiles are collected, the data can be combined into a 3D model of the subsurface, which can help resolve questions about the construction sequence of a site.
Twin-probe (plan-view) resistivity survey is relatively straightforward to carry out. It doesn’t require as much skill on behalf of the instrument operator as magnetometry does. It is however, slow and laborious. The equipment is relatively cheap, and data processing and visualisation are relatively simple. This method is rarely used in the commercial sector these days but is an ideal research tool. Community groups have produced excellent research using this technique. The ERT method requires specialised equipment and a trained collector. The background knowledge needed to correctly process and interpret the data is also high.
Ground Penetrating Radar
GPR only made the odd appearance on Time Team, but in the last decade or so advances in computing (mostly increasing miniaturisation of components, and improvements in battery life) have led to a new generation of GPR kit that is more flexible and affordable.
GPR works a lot like sonar or the sort of radar employed by aircraft. A transmitting antenna sends out radio waves focused into the ground. These propagate downwards and are reflected by abrupt changes in the material of the subsurface. For example, when the waves leave a stone ceiling and move into the vault, some of the waves will be reflected back up. Some will continue on, to encounter the floor of the vault, and anything below it. The reflected waves are collected by a receiving antenna (usually in the same ‘box’ as the transmitter, a fixed distance apart). The strength of the returned waves, along with the time (in nanoseconds!) it takes for them to return is logged and plotted. This is a single trace.
Ground Penetrating Radar Survey at Shrewsbury Castle 2019, funded by the CST
The antenna is dragged along a line, and a series of traces are collected at a small interval (usually every 5cm or 2cm), which are combined together to make a profile. This is effectively a vertical slice through the ground. These are a bit difficult to read because the radio waves emit in a curved shape, so they actually travel in front of and behind the antenna, not just directly under it. This creates distinctive hyperbolas in the data. The depth of signal penetration and the size of the objects you can detect varies with antenna frequency. Depending on the frequency of the antenna, you can look very shallowly and resolve things that are a centimetre (or less) across. Very high-frequency antennas are used to assess the structure of concrete in civil engineering or to image different layers in mosaics and floor coverings. Lower frequency antennas cannot resolve smaller anomalies but can penetrate 10m+ to resolve much larger objects, such as former river beds, large walls or banks and ditches.
Groups of profiles collected in parallel lines can be combined together to make a 3D block of data. This can be processed in a way that allows different horizontal depth slices to be examined (as done at Fotheringhays; see time slice). A new generation of GPR system uses lots of antennas in an array to collect very high- resolution datasets (8cm in all directions), or arrays of different frequencies to quickly collect data with good resolution at multiple depths.
GPR requires a skilled operator to plan the work, collect the data and the process and analyse the results, but it is arguably the best technique for investigating Castle sites. This is because it tends to be good at detecting the sorts of things we would expect to be looking for, for example, voids, buried walls, culverts and surfaces. It can also be deployed inside standing buildings, to look underneath floors or behind walls. It can be used over tarmac and concrete (providing the concrete is not re-inforced!) and does well on most geologies, except for certain kinds of clays, and saline environments like estuaries.
The other advantage of GPR is that the data is relatively fast to collect, compared to earth resistance, and a broader range of features can be detected with it. It is also an inherently 3D method and allows complicated below-ground sequences to be visualised and interpreted. I have seen examples of staircases being visible in the data from 3D GPR, for instance. This technique has made the headlines recently, with the publication of a study of an entire Roman city, Falerii Novi, just north of Rome, by colleagues of mine from Ghent University and Cambridge University.
Geophysics and the Castle Studies Trust
Geophysical approaches form an increasing component of research proposals put to the trust, which is excellent to see! Geophysics can help to answer both broad and specific questions about castle-sites, without the potentially destructive process of excavation. Geophysics also has applications for the conservation of sites and planning for their future management. For example, in mapping the integrity of standing walls using GPR, or understanding the soils and material within earthworks to protect them from erosion in extreme weather events. They can help site managers decide whether an intervention is necessary, and can inform the design of any needed work. Geophysics can also play an essential role in the continuing life of these sites as homes or places of historical interest by mapping areas where conservation or building work is planned to ensure nothing is damaged by the work.
To help keep you entertained during this strange and hopefully unique Christmas the Castle Studies Trust has prepared a Christmas quiz. Can you name the castles these pictures are or images are taken from either our projects from all years or blog posts during the year?
Malcolm Hislop, researcher and author, writes about some of the themes of his most recent book.
Often thought as a highpoint of English military architecture, the castles of Edward I and his followers in north Wales hold a special place in hearts and minds of many in this country and abroad. Scholars have spent much time and effort on researching this (relatively brief) episode of intensive castle construction. We feel we know these buildings so well, and yet, notwithstanding the many accounts of individual castles, it is strange to relate that no lengthy general survey of the architecture (as opposed to the building history) has ever been published. Nor, despite presenting an obvious opportunity for furthering our understanding of the manner in which architectural style was formulated and disseminated in the late thirteenth century, have the influences on and of the Edwardian castle been widely discussed.
Conwy. The outer gatehouse and truncated approach ramp of c. 1283 by James of St George.
Edward’s Welsh castles are inextricably linked to the technical mastermind behind the project, the Savoyard mason, James of St George. Castle builders (in the practical sense) tend to be less well known than their patrons. The ones who can be identified are far outweighed by those who remain anonymous. Moreover, a master builder whose career can be reliably reconstructed to a significant degree is a rarity to be cherished. Master James is one such exception, his reputation as an architect of international repute being established in one of the great historical detective stories of the later twentieth century, which did much to personalise the often anonymous process of medieval construction.
Beaumaris. The North Inner Gate of c. 1295 etc. by James of St George.
Master James’ star has not ridden quite so high in recent years. His architectural role questioned, his artistic contribution doubted, James now seems a slightly diminished figure, with only his organisational and planning abilities remaining unchallenged. There were certainly other master builders employed on the royal works who exercised a degree of independence; it is clear too that there were other influences on the royal works in Wales than can be accounted for by Master James’ accumulated experience in Savoy. In particular, what was the part played by Walter of Hereford, the technical and artistic master mind behind Vale Royal Abbey, and resident master at Caernarfon from 1295? These are interesting issues requiring a greater depth of enquiry, but the initial conclusions of a broader than usual sweep of the architecture are that in addition to his organisational and technical responsibilities Master James also exercised a significant creative role.
Duffus. The great tower of c. 1305 built in Moray with Edward’s assistance.
Edward’s crushing of all resistance in north Wales was swiftly followed by an attempt to subjugate Scotland. Building work in Wales was mothballed and James of St George and Walter of Hereford were redirected northwards. The impact of Edward’s invasion of Scotland on castle building in the northern kingdom tends to receive little attention. Most of the royal works were in timber, little survives above ground level, and archaeology has not yet revealed much that can enlighten the subject. On the other hand, it is becoming increasingly clear that there is a good deal more to say about the contemporary building works of his supporters, that survival of which is much greater, and that in a number of instances there was an English contribution to design and construction. The story of Edwardian castle building in Scotland is only just beginning to take shape.
Newark. The river front of c. 1300, probably influenced by Caernarfon.
Another under-researched theme is the effect of the Edwardian castles in Wales on the architecture of England. There has been an understandable tendency to view the years immediately following the Edwardian conquest of Gwynedd as an anti-climax in English castle building, and that there is little continuity from the Welsh project. Yet the craftsmen dispersed, and building went on, not in such concentrated or dramatic fashion, but often in small quiet ways that escape the notice of the wider world. The full extent of this influence on fourteenth-century castle design is yet to be recognised, but it includes both the broader aspects and the smaller details and represents the final chapter in the story of the Edwardian castle.
Malcolm Hislop’s book James of St George and the Castles of the Welsh Wars (September 2020) is published by Pen and Sword. Hardback, 302 pages, 175 colour and monochrome illustrations.
