Geophysical survey at Pembroke Castle

Aerial photo of Pembroke Castle from the west, showing parchmarks (Crown Copyright RCAHMW, AP_2013_5162)

New work by Neil Ludlow and Dyfed Archaeological Trust (DAT) has revealed the remains of long-vanished buildings, and other features, at Pembroke Castle. Pembroke is famous for its large round keep, built by earl William Marshal, and a number of stone domestic buildings are preserved in the inner ward. But the large, outer ward has been an empty space since at least the eighteenth century.

In 2013, routine aerial photography, by Toby Driver of the Royal Commission on the Ancient and Historical Monuments of Wales (RCAHMW), revealed a number of ‘parchmarks’ in which the outlines of buried walls could be seen, as shorter grass, in the castle. He contacted Neil, who applied to the Castle Studies Trust for a grant to carry out further work at the castle. Thanks to their funding Neil, in partnership with DAT, was able to undertake a full geophysical survey of both the inner and outer wards in May 2016.

Three different methods were applied. Magnetometry, which measures magnetic variation below the ground, was carried out by DAT while Tim Southern undertook resistivity survey, which measures electrical resistance, on DAT’s behalf. Both processes can reveal buried walls and ditches and Ground Penetrating Radar, which can detect features to a depth of over 1.5 metres, was also undertaken in the outer ward, by Tim Fletcher of TF Industries Ltd..

Plans of Pembroke Castle showing the parchmarks and the results of the geophysical survey. Copyright Dyfed Archaeological Trust and TF Industries Ltd.; Crown Copyright RCAHMW.

Survey in the inner ward suggested that two or possibly three previously unknown buildings may lie beneath the grass, but they couldn’t be dated or characterised. At least one of them may, however, be connected with food preparation as neither a kitchen nor bakehouse has yet been conclusively identified at the castle, which would have been necessary to feed the people who made up the earl’s household, his retinue, and the garrison.

The results in the outer ward were outstanding – and surprising. Even allowing for later disturbance, which was slight, the area seems to have been largely empty of buildings during most of the Middle Ages – in contrast to the busy, congested scene that’s normally imagined. This area was enclosed with an impressive curtain wall and towers in the mid-thirteenth century but may always have been envisaged as an open space – for ‘civil’ assembly, for military gatherings, for pageantry and display or for leisure, or perhaps all four; a garden was certainly present by the fifteenth century, and may have been laid out around 1300-20.

Some buildings were however present. A large rectangular building M against the southwest curtain wall, and a possible smaller lean-to N against the southern curtain, are both probably medieval; was the large building for storage, or was it domestic? To account for the apparent absence of a well in the castle, a number of local stories had developed including one which involved a system of water-pipes; the discovery of a possible well, O, may solve the mystery. Most exciting of all was the confirmation that an arrangement of parchmarks G, recorded in 2013, belong to a free-standing, winged mansion-house. Its form suggests that it’s from the late fifteenth century, and it may have been the building within which King Henry VII was born, which is known to have stood in the outer ward.

A ditch formerly separated the outer ward from the inner ward, and a buried masonry structure K, opposite the inner gate, may be a bridge abutment. This ditch was possibly infilled to improve the setting of the fifteenth-century mansion, and garden. Alternatively, the infill may belong to the Civil War period (1642-48) when the castle was held against the Crown, and then against Cromwell. Two former buildings A and B, which overlay the infilled ditch, may date to the Civil War; one of them was associated with a below-ground ‘passage’ that may be a gunpowder magazine. The castle again saw military use during the Second World War, when five ‘Hall-huts’ C were built to house troops based at the castle.

While a number of the other features denote modern service trenches, some may belong to early use of the castle site. A linear feature J may represent the boundary of a burgage plot, perhaps confirming that the outer ward was laid out over part of the town; if so, some of the patchwork of smaller, formless features may also be urban in origin. Others may be hints of prehistoric occupation.

While the results show what can be achieved through geophysics – and generous grant-aid – more work is required before they can be fully understood. In particular, even limited excavation in the mansion may confirm its date and form, and suggest how the outer ward was used during the fifteenth century. The mansion seems to have contained a latrine, so with luck some good palaeoenvironmental evidence has been preserved. Pembroke is a castle of national significance, both architecturally and as a setting for major historic events: it will repay close study.

Pioneering geophysical techniques

Some of the Castle Studies Trust’s projects have made innovative use of cutting edge technology. Nick Tarr explains how a new survey technique was used this year at Pembroke Castle.

Geophysical Survey Technologies (GST) was formed to improve survey equipment for archaeologists to use in all environments including equipment suitable for use in woodlands. The equipment, ideally, should be within the financial reach of amateur groups.

The prototype survey frame resulted from research into voltage surveys (commonly called resistance surveys) where geology or other conditions are unfavourable for conventional methodology. The frame uses a commercially available data logger and power supply but has all four electrodes on a compact mobile frame which is collapsible to fit in boot of a car.

Photo ©Nick Tarr
The prototype frame in use. Photo ©Nick Tarr.

The version used at Pembroke Castle was aimed at keeping the energy from the power supply within the archaeological layers so maximising any opportunity of detecting any archaeology present. A comparison with the conventional twin array in both parallel and zig-zag walking modes was made over a single grid which contained part of a building and a track. The existing twin array frame gave no clear signal for the building, the track was the only major feature seen.

The metal prototype frame. © Nick Tarr.
The metal prototype frame. © Nick Tarr.

The prototype frame gave much better results. A further test across a monastic site in west Wales has also shown improved results over the conventional twin array methodology. Development work continues.

Art as history

Recently a re-examination of an 18th-century painting of Caus Castle in Shropshire helped piece together some of the castle’s history. It was prompted by mentioning the ongoing work at Caus on social media which shows how valuable it can be and how people can get involved.

Paintings and drawings are a useful resource, and while they are typically not meant as a pinpoint accurate record of what they depict, they can offer a guide. When used carefully they can be a very useful resource. There are wonderful medieval miniatures, including details of the siege of Bedford Castle in 1224 and this 14th-century image of a siege.

Some of my favourite images are by the Buck Brothers, engravers working in the mid-18th century. Their images are just wrong enough to remind you that these are not infallible records, but good enough to show how these buildings looked more than 250 years ago.

The National Library of Wales has digitised some of their collection and made it freely available online. With that in mind, here are a few historic images of Holt and Pembroke Castle, all of which are in the public domain.

Announcing our grants for 2016

The Castle Studies Trust is delighted to announce the award of two grants for 2016:Pembroke Castle keep

  • Pembroke Castle – geophysical survey of the castle’s interior. Best known for its massive round keep built by William Marshal, the greatest knight of his age, little else is known about what exactly was in the castle’s interior. Dyfed Archaeological Trust with the guidance of well-known castle expert Neil Ludlow will use the latest geophysical techniques including ground penetrating radar to try and reveal some of the secrets.
  • Caus Castle – earthwork, geophysical and photogrammetric survey of the castle. Frequently referenced in medieval research as an example of a Marcher castle and associated failed borough on the Welsh borders, nobody has done any proper analysis of one of the most important medieval sites on the Anglo/Welsh border. This first detailed archaeological analysis will be carried out by Dr Michael Fradley who has previously undertaken ground breaking surveys of castles at Wallingford (Oxon), Sudeley (Glos), and Newhall (Ches) and Giles Carey. The focus of the project will be on the outer bailey where the medieval borough was situated.

Donate to Have Opportunity to Visit the Selected Projects 

Within the next year the Trust will be organising exclusive visits the selected projects during the initial research stages or at completion of them. These visits are only open to those supporters who have donated to the Trust.

If you would like to be invited to a site visit you can donate in a variety of different ways:

Not only will you have the chance to visit the sites you will also be increasing the amount we can give away to more exciting projects like the ones above next year.

2016 grants: who has applied?

The deadline for grant applications passed on 15th December. We’re going through the various projects now. Altogether the nine projects are asking for £38,000. If you have been following us on social media you will have seen which sites have been proposed. For a little more detail, here are the applications we’ve received:

  • Pembroke Castle, Wales – a geophysical survey of the wards. The castle was once owned by William Marshall, one of the most famous knights of his time.
  • Lochore Castle, Scotland – post-excavation analysis of finds. The site was excavated in 2015, but the team need funding for specialist work on their finds.
  • Lancaster Castle, England (1) – wall penetrating radar of the walls of the castle’s Norman keep. The castle was used as a prison until 2011, so until recently there has been little opportunity for investigation of this sort.
  • Lancaster Castle, England (2) – creating drawings and 3D models to help present the site to the wider public.
  • Caus Castle, England – geophysical and photogrammetic survey of the earthworks of this motte and bailey castle. Caus was one of many such castles while can be found in the Marches of the border between England and Wales.
  • Laughton en le Morthen, England – geophysical survey of the earthworks of a motte and bailey castle. This castle may have been built on top of an earlier Saxon hall.
  • Wressle Castle, England – an examination of the evidence for the slighting of the castle in the 17th century and comparing it to other slighted castles in Yorkshire.
  • Codnor Castle, England – create a virtual reality tour of the castle showing how it once would have appeared.
  • Dunamase, Ireland – remote sensing and landscape survey. Like Pembroke was also owned by William Marshall at one point.

The applications have been sent to our expert assessors who will go over them. In January the blog will have more information on the assessment process, so be sure to visit again.

However there is not enough money to fund them all and so if you would like to donate to help us fund more and gain a chance for an exclusive visit to the chosen projects go here: https://mydonate.bt.com/charities/castlestudiestrust