British

Archaeology

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Cover of British Archaeology 89

Issue 89

July/August 2006

Contents

news

Sensational new discoveries at Bryn Celli Ddu

Missing royal table discovered in Westminster Hall

Unprecedented divide over Stonehenge

DNA surprise: Romani in England 400 years too early

Drama of Shrewsbury's lost medieval bridge

In Brief

features

Balloon over Stonehenge
Martyn Barber considers a photo taken 100 years ago.

Discovering Scotland
Dave Cowley looks back on 30 years of air photography.

Forgotten hero
Miles Russell finds Nero in England.

on the web

Recommended websites

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Views and responses

CBA news

Headlines from the CBA office.

 

ISSN 1357-4442

Editor Mike Pitts

features

The flying Scotsmen

Aerial archaeologists rapidly progressed from seeking out unusual views of standing monuments (previous feature) to the discovery of remains invisible from the ground. In Scotland archaeologists are celebrating 30 years of intensive air photography. As Dave Cowley explains, the programme continues to transform the country's past.

Plough-levelled historic sites can be recovered from the air across large areas when warm, dry weather produces stress in arable crops and (more rarely) grass, revealing buried features through differential growth – or cropmarks. Such archaeological aerial survey in Scotland began in the 1930s with OGS Crawford's pioneering flights, followed after the second world war by that other trail blazer of aerial survey, the Cambridge-based JK St Joseph. It was 1976, however, when Gordon Maxwell and Humphrey Welfare set up a sustained programme of flying at the Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS).

1976 happened to be an unusually hot and dry summer. From the air on June 16 in a flight across the Lothians and Berwickshire, the value of the programme was immediately apparent. During the 30 years since, what became an annual survey cycle has revolutionised our understanding of Scotland's past – especially in the lowlands where centuries of farming have levelled the majority of archaeological sites and monuments.

The RCAHMS aerial survey programme has now undertaken some 1,100 sorties, producing over 100,000 images. Strategy has widened from a close focus on summer flying to take in all aspects of recording, interpretation, understanding and presentation of Scotland's built heritage. An anniversary is a good opportunity to take stock.

In the Scottish lowlands, as nowhere else, aerial survey has populated the landscape with thousands of sites that we have no other effective means of finding: in many arable areas over 90% of them have been recorded only as the cropmarks of ploughed-down monuments. These discoveries have been hard won through years of patient reconnaissance. The vagaries of weather and cropping patterns mean that at any moment only patches of the landscape have the right conditions to reveal sites.

If survey is a slow and painstaking process, this programme has nonetheless been extremely successful. There are whole classes of monument and large areas of early settlement that are on record here only because of the summer flying programme.

Cursus monuments – large neolithic ritual enclosures – are a prime case in point. These are a major facet of the neolithic, and must often have been significant features in the landscape. Yet all but two of the nearly 50 examples now known in Scotland are entirely plough-levelled.

Inevitably the many cropmarks raise questions and challenges to interpretation. The iron age pit-defined boundary is a good example. These curious systems in East Lothian, comprising closely-dug pits arranged in a string of beads manner, emerged in the early years of aerial survey and led to an expectation that the whole of the coastal plain had been enclosed by the late iron age at the end of the 1st millennium BC. In fact, ongoing survey has shown that their distribution is limited to discrete clusters. The boundaries' disposition, with a broad pattern of iron age specialised land-holding emerging, reflects the area's economic and political structure.

It is important to maintain such rolling surveys. New discoveries continue to be made, even in the face of indifferent or poor summers. Two recent spectacular examples illustrate this very well, both from Fife, immediately to the north of the Firth of Forth in an area frequently overflown. AtReedileys in the Howe of Fife we discovered a pit-defined cursus during an otherwise disappointing flight, in a sea of previously recorded sites in a field that had never before been productive. At Oldlord we found an iron age fort whose ramparts incorporate timber palisades and extend out of the responsive arable crop into grass cover, where the defensive circuit is not visible.

A survey programme is not just about putting dots on maps, however, but should always extend to analysis, interpretation and understanding of the past. Questioning what is being discovered keeps the survey process fresh and ensures its continuing relevance.

Aerial mapping is a vital component of analysis. At RCAHMS this is undertaken by my colleague Kevin Macleod using the Aerial 5 computer rectification programme. This corrects an oblique view to a plan view that can then be used as a base for highly accurate interpretative mapping and depiction of sites. Area mapping, such as that in East Lothian where interpretative mapping over an area 10km×20km has been completed, has a number of benefits. It provides accurate locations for site records, a digital map and depiction for interpretation and a base map to inform future survey, where the airborne survey can compare what is known with what can be seen on the ground, and can target the gaps.

Working digitally offers a means of visualising sites such as the illustrated example of a fort at Hanging Craig. The rectified aerial photo and derived mapping are draped over a digital terrain model, which nicely shows the local context of the site. This is both a valuable interpretative tool, and a powerful means of presenting plough-levelled archaeological sites, where by definition there may be nothing to see on the ground.

Gaps in coverage

Important as they are, cropmarks do not constitute the only focus of our aerial work. The benefits of an overhead perspective for recording standing earthworks were early recognised in the RCAHMS programme. Raking light and low vegetation can bring out detail difficult to resolve from ground level, greatly aiding interpretation and presentation.

Here the value of combining oblique aerial photography with block vertical photography is clear. Continuous and extensive vertical shots afford the wider view, while targeted obliques add detail. The integration of these sources is an important means of ensuring a comprehensive coverage and maximising the return from an area.

It also highlights that survey work should not just be conceived of as the reconnaissance phase of buzzing about in a small plane. It is a rounded undertaking that involves looking through complementary sources such as existing vertical block photography, of which RCAHMS holds over 1.5m images. Many of these were taken by RAF crews in the 1940s and are a valuable record of the Scottish landscape before the changes effected by the intensification of agriculture in the second half of the 20th century.

Our remit has extended across the length and breadth of the country, taking in everything from the first monuments to 21st century architecture, as well as broad landscape character. Buildings and urban landscapes have responded well, as shown in the popularity of books on towns and cities seen from the air.

We recently decided to upgrade the aerial record of grade Alisted buildings. This began with a project to help fire brigades. Fire officers found the aerial perspective useful in evaluating buildings, and learning more about matters such as access and local water supplies. This highlighted the many gaps in our national collection of photography, and a pressing need to cover the major architectural monuments as comprehensively as possible. Such identification of gaps or bias is an important part of taking stock and maintaining the relevance of the aerial survey programme.

Archaeological recording has developed a concern with landscape over the last 20 years, seen also in the aerial survey team's images that evoke the rich tapestry of rural Scotland. In particular, illustrative material collected in support of the Historic Landscape Assessment project is roving a valuable reference collection of landscape variation.

Essential resource

East Lothian, where most of the known archaeological monuments are plough-levelled, is one of the lowland areas where the impact of flying has been most felt. Yet significant gaps in the distribution remain even here, on poorly drained soils less likely to produce cropmarks. Exploring these gaps is one of the challenges for future survey, in particular concentrating effort into them when extreme dry conditions present themselves.

Awider and pressing need is to fly in all areas and redress the regional biases. The concentration of RCAHMS flying in the south and east of the country is due largely to the programme's origins in summer cropmark flying, as most arable ground lies in this area. So recently there have been two aerial campaigns on the Western Isles, not previously overflown by the RCAHMS (the very few existing oblique images dated from over 20 years ago). The programme aimed to record all major monuments and a cross-section of types of remains, from fish-traps to brochs and crofting settlement. Thus well-known and lesser-known monuments have been captured alongside contemporary settlement, and views to explore landscape character.

The Scottish aerial survey programme was set up to explore the archaeological potential of the lowlands for plough-levelled sites visible as cropmarks – and in this it has changed our understanding of these areas out of all recognition. As the subject matter has diversified into earthworks, architectural subjects and landscape recording, aerial survey and photography have established themselves as valuable tools in understanding Scotland's past.

Moreover, a resource has been created whose value can only grow as Scotland's landscape changes: it is a goldmine that can be revisited as perspectives and personnel change. This is an aspect of working with aerial photography that has recently turned up a nice surprise. While answering a routine public enquiry on a photo that had lain in the archive for over a decade, Peter McKeague discovered a Roman temporary camp at Raeburnfoot in a shot taken of a different monument that happened to be on the same hillside. Effective aerial survey is organic. It draws on both new reconnaissance and existing resources.

Dave Cowley is the aerial survey manager at RCAHMS and chairman of the Aerial Archaeology Research Group. AARG will be holding its annual conference in Bath Sept 11–13 (aarg.univie.ac.at). He is the co-editor (with Kenneth Brophy) of From the Air: Understanding Aerial Archaeology (Tempus 2005, ISBN 0752431307)

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