Tag Archives: Geophysical Survey

‘In the castle called Seresberi’. Old Sarum and a New Survey of the Inner and Outer Baileys

John Constable's watercolour of Old Sarum, showing the scale of the outer ramparts and the Norman motte (source: Wikicommons, http://commons.wikimedia.org/wiki/File:John_Constable_-_Old_Sarum_-_WGA5198.jpg)

John Constable’s watercolour of Old Sarum, showing the scale of the outer ramparts and the Norman motte (source: Wikicommons, http://commons.wikimedia.org/wiki/File:John_Constable_-_Old_Sarum_-_WGA5198.jpg)

Old Sarum in Wiltshire has always proved an emotive archaeological site. The substantial ramparts of the Iron Age hillfort and the medieval motte dominate the skyline on the A345 running north from Salisbury, and has been portrayed by scholars and artists including Stukeley and John Constable. The palimpsest of settlement at the site and in its environs encompasses the Iron Age and Romano-British periods, possible Anglo-Saxon settlement, and the medieval founding of a castle, cathedral and settlement. The site formed part of the rotten borough of Old Sarum, and its strategic position was utilised during the Second World War. The Inner and then Outer Bailey formed the focus of excavations in the first part and middle of the 20th century, first by Hawly , Hope and Montgomerie in the years preceeding the First World War, then by Rahtz in the 1940s and 1950s.

The work of Hawley and Hope commenced with excavation of the Inner Bailey in the earlier seasons. Excavation then extended to the Outer Bailey, with the 1914 season focusing on the Cathedral and Bishop’s Palace. The excavation report indicates the presence of structural remains beyond those currently visible at the site, with a number of the lesser structures having been backfilled. The later work by Rahtz focused on the ramparts of the Outer Bailey and the tunnel running through the northern section of the ramparts. The body of work left from the excavations provides ample evidence of the nature and depth of the archaeological deposits for both the Inner and Outer Baileys, although the focal point of the work was always trained on the more substantial or higher status structures and buildings of the site. Much of the urban plan of the Inner Bailey, including the Palace, the Keep and Postern Tower was revealed, although some scintillating glimpses of structures from earlier periods, including a possible Roman building some 5m below the modern ground surface, were also gained. In the Outer Bailey the excavations revealed considerable structures for the cathedral and Bishop’s Palace, but much of the area in the other three quadrants of the Outer Bailey remain a mystery. On the basis of the known archaeological evidence for the site it was decided that application of topographic and geophysical survey techniques would assist in mapping the buried remains across the remainder of the Outer Bailey, and the unexcavated parts of the Inner Bailey.

To that end staff at the University of Southampton drew up a three year project overview, and were granted permission from English Heritage, to carry out a new survey at the site and in its environs as part of student fieldwork for second and third year modules in archaeological survey and geophysical survey. Results of the survey would form the basis for students to compile their own reports for assessment on the modules.

Geophysical survey in the Outer Bailey with the spire of Salisbury Cathedral visible in the background

Geophysical survey in the Outer Bailey with the spire of Salisbury Cathedral visible in the background

The work of the staff and students this year centred on the area within the ramparts of the hillfort, some 6.5 hectares in size, with topographic survey and earth resistance and magnetometry being conducted in the Outer Bailey, and GPR survey across the Inner Bailey to target areas left unexcavated by Hawley and Hope. Survey was supervised by the author, Timothy Sly, Dominic Barker, Penny Copeland and Scott Chaussee.

Magnetometer survey in the Outer Bailey with the bridge to the Inner Bailey in the background

Magnetometer survey in the Outer Bailey with the bridge to the Inner Bailey in the background

Earth resistance survey in the Outer Bailey

Earth resistance survey in the Outer Bailey

In spite of the mixed success using magnetometry at some sites in Hampshire and Wiltshire, the nature and depth of deposits at Old Sarum meant that the flint core and stone buildings of the Outer Bailey contrast well to the surrounding sediment. In addition the response to the earth resistance survey was also clear. The preliminary results for the Outer Bailey indicate extensive structures across the entire area, with buildings spread out along the curtain wall, particularly in the south-east sector of the site, and the pattern of urban areas visible in the south-west sector.

Detail of the results of the magnetometry from the Outer Bailey

Detail of the results of the magnetometry from the Outer Bailey

Many of the structures from the Hawley and Hope and Rahtz excavations are also present, and new buildings are added to the plan of the north-west sector of the site, including a possible sub-circular structure.

The GPR survey in 2014 focused on the area of the Inner Bailey, utilising a 200MHz antenna, and on targetted areas in the Outer Bailey using a 500MHz antenna. In principle the use of the lower frequency antenna within the Inner Bailey should assist in locating some of the deeply buried structures below the level of medieval buildings mentioned in the literature. Potentially comparison of these results at 5-6m depth should allow a picture of the Iron Age and Roman deposits for the area to be compared with the results from the Outer Bailey.

GPR survey of the Inner Bailey. Many of the excavated structures give a clear indication of the potential depth of some of the deposits, up to c.5m in places. The 200MHz antenna should allow structures to be located down to these depths

GPR survey of the Inner Bailey. Many of the excavated structures give a clear indication of the potential depth of some of the deposits, up to c.5m in places. The 200MHz antenna should allow structures to be located down to these depths

In addition to the high resolution survey work, an Electrical Resistivity Tomography (ERT) profile was run across the site, through the western entrance to the hillfort, skirting the northern side of the motte ditch, and ending close to the ramparts on the north-eastern side of the site. The profile is designed to assess the depth of archaeological sediments across the site, and their relationship to the underlying gravels and chalk.

ERT survey in a profile running across the site

ERT survey in a profile running across the site

There is much work to do for the interpretation of the results, but the correlation between the 20th century excavations and the latest results is telling. The results are allowing the team to expand on the excavation plans, showing the presence and nature of the new structures in all areas of the site, including ranges of buildings on the southern edge of the area of the Cathedral, and a substantial building standing alone in the south-eastern sector of the Outer Bailey. The plan for the next few seasons will be to complete work in the Outer Bailey, and to conduct survey in the environs of Old Sarum. The relationship between the defended site and the Roman road and settlement to the south of the ramparts will provide a focus for research.

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Survey and Excavation at Cranborne Chase

After a few weeks of survey in the New Forest, teaching of practicals and writing up of some papers, it was good this week to get back out in the field with staff and students from the University of Southampton. This time we headed out to Dorset for excavation and survey at Down Farm on Cranborne Chase, with teams of students involved in excavation, finds processing and recording, together with some topographic survey and magnetometry. weather during the course of the week was beautiful, strong sunshine with a light breeze moving over the hay meadows, with skylarks singing in the sky, reminiscent of surveys and excavations in the past on moorland in the north of England.

Students excavating on the main trench.

Students excavating on the main trench

The group were divided into teams for excavating of 1m by 1m test pits  along a low lying ridge to the south of the farm, with others excavating a larger trench with pit and postthole features. Some studetns also commenced surveying, with magnetometry being conducted in the area around the main trench. The ground offered perfect conditions, although generations of plough damage and truncation of the ploughsoil suggest that remains in the area may be quite ephemeral.

Dr Alison Gascoigne moving strings during the magnetometer survey

Dr Alison Gascoigne moving strings during the magnetometer survey

Excavation of the test pits

Excavation of the test pits

The pla nover the next week or so with the magnetometry is to cover as much of the southern part of the field as possible, mainly as a training exercise, but also to locate any other posssible features that might make useful targets for excavation. The trenches, supervised by Tim Sly, Dom Barker, Cat Cooper and Sam Giffiths are revealing features broadly Iron Age in date, mainly pits and postholes, vut directly into the natural chalk. There is, however, real scope for much more extensive geophysical survey and topographic survey across the landscape at Down Farm. Given the nature of archaeological remains and the underlying geology, similar to that of Tidgrove Warren Farm in Hampshire, large-scale survey would provide some solid foundation data for analysis and targeted excavation.

One of the undergraduate students conducting magnetometry

One of the undergraduate students conducting magnetometry

The excavations and survey will continue next week together with magnetic susceptibility survey to broaden the survey coverage using a lower spatial resolution of survey. Topographic survey started on Wednesday using Smartnet GPS. The cellphone coverage for the area was, however, insufficient for operating Smartnet, and on Thursday standard RTK survey was coducted. The trenches and topography for the area will be surveyed in using this.

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Spring Survey – Week 2 Review

Smashing blog from Nicole Beale on the completed survey at Basing House, and a bit of a low-down on the techniques used, represented by abbreviations and three letter acronyms in my blog over the last few weeks. Enjoy!

Basing House Project

The undergraduates have finished working at Basing House for this Spring, and we’ll be back on site in a few weeks to collect  more data for some of our postgraduate students who are using the site for various projects.

This is the team from Week 2. I can’t believe how much ground these guys covered! Thanks all!

I thought it might be useful to give you a rundown on the different tools that we were using to record the site during the topographic, building and geophysical survey, as we keep saying things like ‘mag’ and ‘GPR’ without explaining what any of them are!

In our next post, we’ll begin to share the results of the surveys, so do check back regularly, or subscribe to the blog for updates, using the link on the navigation to the right.

Geophysical Survey

There are a few pieces of kit that we use for…

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Wanderer’s Return

Just got back from continuation of the GPR survey of Late Period and Roman Necropolis at Quesna. A hectare of survey data to be processed prior to excavation, more links and information to follow in the next few days.

The excavation and survey for the Kingsclere Parish Archaeological Project (KPAP) is due to kick off next Tuesday. The work will include geophysical survey of the site and landscape surrounding a Romano-British settlement, including a multi-vallate enclosure feature and rectilinear platform visible in 1940s air photographic images. Students and staff at the University of Southampton will be involved, and volunteers from the Kingsclere Heritage Association. The plan is to set up a blog here for the duration of the excavation, to post up daily updates and photos from the dig. Watch this space for more details.

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