ARCHAEOLOGICAL FIELDWORK AT BAMBURGH

When investigating a site such as Bamburgh Castle, which is of outstanding archaeological importance, it is vital to conduct the work in a very careful and methodical fashion. The first part the investigation has used non destructive survey techniques as the principle means of investigation. These techniques have included the use of geophysical survey in conjunction with mapping and recording of the castle structures by EDM (electronic distance measurer), which is a type of electronic theodolite with which measured surveys can be conducted with great accuracy in all three dimensions.

Surveying with an EDM

The reason for the extensive use of geophysical survey, initially, is fairly simple, excavation, which most people imagine when they think of archaeology, provides a tremendous amount of detailed information but it is destructive and an experiment that can only be conducted once. Geophysical survey however disturbs nothing and can provided invaluable advanced knowledge on which we can base future work.

Geophysical survey

So far perhaps the most exiting results have emerged from a resistivity survey conducted, by Phil Howard of Durham University, on the extensive area of lawn within the Inner Ward.

Resistivity involves conducting a small electric current into the ground through metal probes in order to measure subtle variations in electrical resistance over a given area. As you can imagine a stone wall does not conduct electricity very well and will show up as high resistance. Conversely material which had accumulated in a ditch is likely to have retained a relatively high moisture content and will show up as a lower than normal resistance. By taking a large number of readings over a measured grid a plan of buried features can be compiled even though on the surface nothing can be seen but a uniform turf or topsoil.

A number of linear features have been detected, and although the results were too faint to outline complete buildings, that the linears represent parts of structures seems in little doubt. The resistivity plot and the interpretation of the data is shown below.

The rectangular anomaly marked (A) looks very like a building and two sides of a further structure (B) has shown up to the north-west. The other linear features in the survey may indicate the presence of other structural remains, though somewhat poorly defined. The fact that the alignment of the structures is very different to that of the existing structures of the castle and those of the known medieval arrangements is perhaps very significant. What were these structures then, and perhaps more importantly when where they? Given that they are unlikely to be either medieval or post-medieval the most logical interpretation left is that they date to the Anglo-Saxon period and that in the ghostlike linear alignments on the resistivity plot from the Inner Ward we have our first view of Northumberland’s Anglo-Saxon capital to emerge in 1000 years.

At the same time as the resistivity survey on the lawn a further such survey was conducted within the Chapel of St Peter. Here features were again identified, though their interpretation has proved difficult. The foundations of the chapel seen today are the remains of the building constructed during the reign of Henry II and are believed to lie on the site of the earlier Basilica of St Peter.

The resistivity may have shown up some traces of this earlier structure, though not in a clearly identified form; or the results may represent structural alterations conducted in the lifetime of the later 12th century chapel. A clear interpretation must await further work.

A magnetometry survey of the West Ward was also conducted during this phase of work. Magnetometry works along similar principles to resistivity, though detecting minute anomalies in the earth’s magnetic field caused by the variable magnetic character of certain types of buried feature. These results although interesting were harder to interpret. A number of large sub-circular anomalies were distributed in the southern part of the survey area and could conceivably represent pits and be of archaeological origin.

Ground penetrating radar survey

An extensive radar survey was conducted, by Brian Donnelly of Northumbrian Surveys, within the Inner Ward of the castle in order to check and further expand on the resistivity survey. The survey has recovered a vast volume of data and has confirmed the presence of a number of the structures seen on the resistivity plot. In addition it appears to have picked up a substantial boundary-like feature towards the east end of the ward, to the the rear of the chapel of St Peter. One very tentative interpretation for this could be that the main area of secular occupation of the castle was deliberately segregated from the area of religious activity by this boundary.

Radar survey was also conducted within the chapel where it has produced some very exciting results. A number of point anomalies located within the main body of the building could well represent grave markers for individual burials. The most fascinating results of all were seen at the west end of the building where a number of survey lines identified a substantial feature extending across the width of the building and 5m into the body of the chapel. A 3D computer projection of this feature showed a vault-like shape, extending more than 2m into the ground.

Further radar suvey work within the west wared of the castle and on the cricket pitch in front of the castle has been conducted as part of the community based survey project. The results of this work are providing new insights into both the medieval castle and previous excavations conducted at the site.