The Butser Ancient Farm Earthworks Research Project
A first analysis of the data and a description and review of the methodology
Dr P J Reynolds and R W Hedge C.Eng.
Summary
This Monograph reviews the background to setting up this long-
Evidence is given to demonstrate that the initial stabilisation of a freshly dug experimental ditch and bank system, in chalk grassland, is effectively complete by the seventh year after preparation. The relative importance of grasses in this process, in comparison with other vegetation, is discussed. A simple algebraic expression to show the effect of differential erosion of different faces on the pattern of in-
This work, taken in comparison with other earthworks, has shown how and, perhaps more importantly, why earthworks of different designs behave differently, using simple concepts from particle mechanics. It should enable more certain interpretation of features of field records from earthworks. Prospects for both future studies and additional data analysis are discussed.
Introduction
Since one of the most typical remains of past peoples in the landscape is the ditch and bank, whether of monumental proportions like those around major hill forts or castles or minor traces on the ground indicating lesser settlements, it has always evinced great fascination. There has always been a major focus upon such earthworks, especially since it has been believed that the most reliable dating evidence will be gained from the layers in the ditch. In fact, a large number of sites has been excavated with only the ditch having been sectioned. The internal zones have been left entirely untouched. It was also believed that the interiors would have been so disturbed by subsequent periods that only the surrounding earthwork has been scheduled for preservation. Recently, over the last thirty years, this has been realised to be untrue and several major excavations have demonstrated the wealth of evidence to be recovered.
Nonetheless, fascination with earthworks has not significantly abated. Late last century General Pitt-
In 1960, a new departure was initiated with the construction of a monumental earthwork at Overton Down, Wiltshire, UK. This was a product of a group of leading archaeologists in Britain who were interested in the processes of construction but, more particularly, in what happened to such an earthwork through the passage of time and, further, in what happened to materials buried in the bank of the earthwork. It was also the first time that an extremely long term experiment had been designed insofar as it would outlive its progenitors by some considerable time. The proposal was that the ditch and bank would be regularly sectioned after one year, then two years, then four years and thereafter on a binomial progression until one hundred and twenty years had passed. Currently the thirty-
This earthwork was constructed on Upper Chalk on the open Downs. In 1963, a second earthwork of exactly similar proportions and design was built on the sands at Morden Bog, Wareham, Dorset, UK and which has received the same study approach as at Overton. Both earthworks are linear and, specifically, they simulate prehistoric territorial boundaries where the bank was set at some distance from the ditch, thus creating two elements, which appear to behave as independent entities, rather than an integrated unit. With the advances made in scientific archaeology over the last decade, especially with regard to soil sciences, these earthworks are providing a wealth of invaluable data to enhance the understanding of the archaeological evidence from actual sites. There has been a recent overview of the history of the two, covering the background in more detail (Ashbee & Fowler 1998). In 1976, another experimental earthwork was created by Reynolds with a totally different purpose. The object was to simulate the typical ditch and bank which surrounded small settlements of the Bronze Age and Iron Age in order to examine the erosion patterns insofar as they create specific layers in the ditch profile when excavated. In this case the ditch and bank were integrated together so that they formed an entity. In effect it proved to be a pilot scheme. The ditch and bank formed an enclosure which was the focus of the museum area of the Butser Ancient Farm.
Rectangular in plan, it was based upon an actual Iron Age earthwork at East Castle in Dorset. The ditch was dug with a V-
It was soon realised how critical the weather was in terms of simple erosion. However, what proved to be most remarkable was the speed at which vegetation began to encroach. Since the ditch cuts through the topsoil, a face is left from which plants immediately begin to germinate. Similarly the surface of the berm, which was grassland and despite the construction of the earthwork is largely undisturbed, becomes a reserved area, in that neither people nor animals walk or graze there. In consequence the grass grows abundantly and, in contrast to a meadow or paddock, where the grass is cut or eaten, it reaches maturity and seeds. These seeds fallin situ and germinate in due season. On the bare chalk faces of the ditch, within a few short weeks algae and mosses began to grow. These formed discrete catchment zones for particles of soil which tumbled from the soil profile and thus provided niches of nutrient for seeds to exploit. A similar phenomenon was observed during the first four years at Overton (Jewell and Dimbleby 1966). There, it was noted that little or no evidence existed for this effect aiding in the establishment of other plants. Any positive effect, such as seen by Reynolds at L'Esquerda, may be small and very site specific.