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Mending the Mound: Recent Work at Silbury Hill - Jim Leary, English Heritage

A presentation by Jim Leary, of English Heritage, given as part of the autumn seminar series at the Division of Archaeological, Geographical and Environmental Science, at the University of Bradford. The subject was Silbury Hill, one of the most enigmatic ancient monuments in the country, and an imposing presence in the Wiltshire landscape.

Previous excavations

Archaeologists have been fascinated by Silbury Hill since Aubrey took King Charles II to admire the Hill in the 17th Century.  The earliest excavation attempt was carried out by Edward Drax in 1776, which left behind a crater at the summit, the result of the digging of a large shaft down into the depths of the Hill. In 1849 a tunnel was dug from the side towards the centre, by John Merryweather

image00202In 1968 the BBC sponsored a new excavation of Silbury Hill under the supervision of Richard Atkinson, to be televised live.

This was a milestone in broadcasting history, attracting huge audiences and raising false expectations for the discovery of a fabulous treasure hoard, which never materialised.

1968 Atkinson’s Findings

Back in 1968 Richard Atkinson identified three main construction phases:
Silbury I – small mound about 5 metres high and 8 metres diameter, using organic materials
Silbury II – Building up the mound to a height of 25 metres, using chalk extracted from the surrounding ditch
Silbury III – Further build-up to create the hill we see today, and the digging of a larger quarry ditch

Now, in 2008, English Heritage have just completed a re-investigation of the Atkinson tunnel, and the preliminary results were presented at the University of Bradford seminar.

Why the latest investigation?

In May 2000 a gaping hole appeared on the top of Silbury Hill, expanding in size at an alarming rate. It transpired that the tunnels of the old excavations by Atkinson and Drax were never properly backfilled and the internal voids were now collapsing.

English Heritage took action to open up the tunnels in order to shore them up and backfill them properly, thus stabilising the ancient monument. Of course, this presented the ideal opportunity for archaeologists to take environmental samples, take detailed digital images, and make one last examination of the Hill’s construction.

2007-2008 findings by English Heritage

Leary now believes that the Hill was built incrementally, with at least 20 identifiable construction phases. By analysing soil samples and stratification accessible from inside the old Atkinson tunnel, Leary believes the development of the Hill may have begun with a stone enclosure around a Neolithic ritual site (indicated by a “truncated”, trampled soil “horizon” containing signs of a possible hearth).

The first low gravel mound constructed over this ritual site was the first of many layers added by successive generations, each gradually making the mound higher and wider. At first, organic material was used, such as soil and turfs. Stake holes indicate the edges of the mounds were probably demarcated by wooden posts. There appear to have been gaps in the building process, when, rather than covering the whole mound with a new layer, people preferred to dig pits into the existing mound, in which have been found deposits of flint flakes, animal bones, burnt flint and yew berries.

There was a satellite mound – an additional small “mini-Silbury” (just 40 cm high) found at the eastern edge of the main mound – there may be several more waiting to be found.

As mound construction was resumed and the Hill was enveloped in more layers of chalk, gravel, turf, mud and soil, it appears to have adopted a new significance. Sarsen boulders and stones were deliberately deposited within the structure.

Silbury from the airSubsequent layers consisted of chalk and clay. A series of 5 banks (the clay and chalk mix probably being quarried out from the surrounding ditch) were built up against the side of the growing mound. But the construction of new layers continued, covering over the Hill and its 5 banks. The surrounding ditch was backfilled and re-cut four times (using large chalk stones to create a dry stone revetting wall to hold in the finer chalk infill – in very similar fashion to the banks at Avebury) to accommodate the growing size of the Hill.

The discovery, within the later layers of Silbury Hill, of discrete clusters of sarsen stones accompanied by antler pieces, again signifies a possible ritual significance.

Dating the Hill is still uncertain – results of radio carbon dating have yet to be confirmed, but appear to place the Hill’s construction to sometime between 2,000 and 2,400 B.C.

Leary’s thesis

Leary disputes traditional interpretations of the Hill’s function as being too hidebound by modern views of monuments as planned constructions with a very specific purpose and significance defined from their very conception. He argues that the site grew slowly, and that as it grew and changed, so did the builders’ own perceptions of the structure. Perhaps the actual structure itself was relatively unimportant – perhaps, Leary suggests, it was the ritual and the ceremony which was more important to them, the monument being a product of the activities associated with those rituals.

He also hinted at other questions which are raised by Silbury Hill – for instance, what were the costs involved in its construction in terms of social organisation, time, the organization of the workforce, etc. And what is the significance of its location – what was its relationship to the wider sacred landscape of Wiltshire (Stonehenge, Windmill Hill, West Kennet barrow, Avebury, are all nearby), to the surrounding natural chalk landscape, and to the local rivers and springs.

And finally, what did the monument mean to later cultures? The Romans built a town and road alongside; 12th or 13th century artefacts and large post holes on the summit of the hill indicate there may have been a substantial medieval building here (which may account for the flat top of the Hill).

Further reading:
Whittle, A. W. R. and Best, J, “Sacred mound, holy rings : Silbury Hill and the West Kennet palisade enclosures ; a later Neolithic complex in North Wiltshire” (1997)

Pitts, Mike  "Silbury is safe". British Archaeology (101): 8., (June 2008), Council for British Archaeology.


English Heritage

Pastscape – (including investigation history and bibliography in the “About this monument” section)

Guardian newspaper report

Wiltshire Sites and Monuments Record

British Archaeology magazine articles - here & here

BBC Wiltshire online

For further details of the research seminars click here



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