Category Archives: Geophysics

Foot of Avebury Down Dig – Day 2

It’s Day 2 and we’ve been dodging the rain a bit today, but thankfully the thunderstorm that threatened passed by to the south. After yesterday’s day of de-turfing, we’ve now started digging into the archaeology in Trench 1 .

This morning, a grid was laid out in the trench and we began to excavate alternate squares.


Trench 1 grid layout ©National Trust/Briony Clifton


The chequerboard excavation of Trench 1 begins – the remaining squares will be excavated later ©National Trust/Briony Clifton


The finds that are coming out of Trench 1 are predominantly worked flint flakes, but today also saw a few sherds of middle Neolithic pottery, known as Peterborough ware.


Peterborough Ware from Andy’s square ©National Trust/Briony Clifton


We also had a visit from Dr. Philippe De Smedt of the University of Ghent this afternoon, who we had spotted earlier in the day driving over the fields to the east of the West Kennet Avenue. He’s been carrying out an Electro Magnetic Induction (EMI) geophysical survey as part of the Living with Monuments Project.


Philippe is the tiny black dot in the lighter-coloured field just upslope from the field of cows ©National Trust/Briony Clifton


Stay tuned for more from the Neolithic…

The Calibration of a Landscape

For the last week the Universities of Birmingham and Ghent have been working hard in the Stonehenge Landscape, carrying out excavations with an interesting twist.

For several years now, Dr. Philippe De Smedt of the University of Ghent has been conducting electromagnetic induction surveys* (EMI) over vast areas of the Stonehenge Landscape. He,  Paul Garwood and Dr. Henry Chapman (both of the University of Birmingham) now want to be able to understand the survey data more clearly by substantiating it through excavation and coring.


Excavation of two of the anomalies in the EMI Survey ©Philippe De Smedt/University of Ghent

Using the data from these surveys, and also coring results from work carried out towards the end of last year, the team are targeting specific features in the landscape for excavation. These features were chosen because of the particular signals they were giving out – some archaeological and some geological. These excavations and comparisons with the survey data will, in turn, support improved interpretation of EMI geophysical data from a calibrated landscape.


Archaeologists from Birmingham and Ghent excavating a large pit ©National Trust/Briony Clifton

The team will be continuing their excavations this week (from Tuesday 4 July until Sunday 9 July) so if you are paying the Stonehenge World Heritage Site a visit, have a wander into the Landscape and see for yourself. On many of the days you will be able to chat to one or two National Trust volunteers who will explain what the team is up to.


Sieving each bucketful ©National Trust/Briony Clifton

*electromagnetic surveying – a type of geophysical survey using electrical conductivity and magnetic susceptibility, measuring properties of the soil and depth levels.

SQUARING THE CIRCLE: Archaeological detectives discover ‘secret square’ beneath world-famous Avebury stone circle

New archaeological surveys reveal unique square megalithic monument at the heart of the World Heritage Site.

Archaeologists have found a striking and apparently unique square monument beneath the world famous Avebury stone circle in Wiltshire.

The UNESCO World Heritage Site, cared for by the National Trust, was built over several hundred years in the 3rd millennium BC and contains three stone circles – including the largest stone circle in Europe which is 330m across and originally comprised around 100 huge standing stones.

A research team led by the University of Leicester and University of Southampton used a combination of soil resistance survey and Ground-Penetrating Radar to investigate the stone circle.

Their work was funded by the Arts and Humanities Research Council (AHRC) and supported by the National Trust, as well as archaeologists from the University of Cambridge and Allen Environmental Archaeology.

Dr Mark Gillings, Academic Director and Reader in Archaeology in the School of Archaeology and Ancient History at the University of Leicester, said: “Our research has revealed previously unknown megaliths inside the world-famous Avebury stone circle. We have detected and mapped a series of prehistoric standing stones that were subsequently hidden and buried, along with the positions of others likely destroyed during the 17th and 18th centuries. Together, these reveal a striking and apparently unique square megalithic monument within the Avebury circles that has the potential to be one of the very earliest structures on this remarkable site.”

Avebury has been subject of considerable archaeological interest since the 17th century. The discovery of new megaliths inside the monument was therefore a great surprise, pointing to the need for further archaeological investigations of this kind at the site. The survey took place inside the Southern Inner Circle, contained within the bank and ditch and colossal Outer Stone Circle of the Avebury henge. Excavations here by the archaeologist and marmalade magnate Alexander Keiller in 1939 demonstrated the existence of a curious angular setting of small standing stones set close to a single huge upright known since the 18th century as the Obelisk. Unfortunately, the outbreak of war left this feature only partially investigated.


Model of square stone setting

A possible reconstruction of the stone settings within the southern inner circle incorporating  Keiller’s discoveries and those of the new geophysical surveys


Dr Joshua Pollard from the University of Southampton said: “Our careful programme of geophysical survey has finally completed the work begun by Keiller. It has shown the line of stones he identified was one side of a square of megaliths about 30m across and enclosing the Obelisk. Also visible are short lines of former standing stones radiating from this square and connecting with the Southern Inner Circle. Megalithic circles are well known from the time when Avebury was built during the late Neolithic (3rd millennium BC), but square megalithic settings of this scale and complexity are unheard of.”

Dr Nick Snashall, National Trust archaeologist at Avebury, said: “This discovery has been almost eighty years in the making but it’s been well worth waiting for. The completion of the work first started by Keiller in the 1930s has revealed an entirely new type of monument at the heart of the world’s largest prehistoric stone circle, using techniques he never dreamt of.  And goes to show how much more is still to be revealed at Avebury if we ask the right questions.”

figure_3 (1)

The reconstructed ground plan of the Southern Inner Circle combining the results of the current survey with the 1939 excavation

The archaeologists who undertook the work think the construction of the square megalithic setting might have commemorated and monumentalised the location of an early Neolithic house – perhaps part of a founding settlement – subsequently used as the centre point of the Southern Inner Circle. At the time of excavation in 1939 the house was erroneously considered by Keiller to be a medieval cart shed.

If proved correct, it may help understand the beginnings of the remarkable Avebury monument complex, and help explain why it was built where it was.

The research team is currently compiling their research into a paper for academic publishing.

You can access a full technical report here


The work was part of the ‘Living with Monuments project’, funded by the Arts & Humanities Research Council (AHRC).  The Living with Monuments project is five years (Sep 16 – Sep 21)  and AHRC funding amounts to £780,831. It is a collaborative project involving archaeologists from the Universities of Leicester, Southampton and Cambridge, the National Trust, and Allen Environmental Archaeology.

The survey was directed by:

Dr Mark Gillings,  University of Leicester

Dr Joshua Pollard, University of Southampton

Dr Nick Snashall, National Trust, Archaeologist for Stonehenge and Avebury WHS

Dr Ros Cleal, National Trust, Curator of the Alexander Keiller Museum, Avebury