The geophysical survey has been completed. Below is an edited version of the report on the resistance results prepared by GSB Prospection Ltd who undertook the survey on behalf of English Heritage and Chester City Council. Some of the uncertainties expressed in the report illustrate how difficult it can be to interpret resistance results in a heavily disturbed urban area.
Below is a close up of the area immediately in and around the Amphitheatre Site.
A broad high resistance band running through the centre of the area is thought to be related to the remains of the concentric and outer walls of the amphitheatre. This interpretation is strengthened by the fact that this anomaly is coincident with the high and low resistance linear trends from modern concrete markers at the surface denoting the position of the walls (these have now been removed). The high resistance zone appears to extend west beyond the outer wall and it is assumed that this is related to the Roman remains. Two high resistance linear anomalies extend south from the main body of the response and, despite showing a smaller contrast with the background as seen elsewhere; they are tentatively interpreted as being of an archaeological origin.
Also in the ‘deeper’ data set, an anomaly appears to follow the line of the current inner wall of the amphitheatre. As the response is set back from the wall it seems unlikely that this is an artefact and therefore may represent a structural feature.
The circular low resistance anomaly with a high resistance centre is curious, and this may be a modern feature. The trend running through it could be associated, but may equally be a facet of the surface markers which crossed the site.
A number of rectilinear trends are possibly of archaeological interest, but again may be coincident with more of the concrete surface markers.
Two low and one high resistance anomalies have been interpreted as an effect of previous archaeological excavations. The smallest of the low resistance responses equates with a trench dug in 2000 and the other two anomalies date from the 1960’s. An anomaly is coincident with a high amplitude anomaly in the earlier radar survey of the site, which was also interpreted as the result of an earlier excavation trench. It is possible that this feature is related to the edge of the vomitorium but the lack of depth extent tends to discount this.
There is a relatively broad high resistance anomaly in the data that given its orientation is likely to be related to the arena’s concentric and outer wall fabric and possibly one of the vomitoria. The depth extent of the anomaly strengthens this argument, although it cannot rule out the possibility that this response relates to St. John’s House and cellars that were located in the vicinity.
In the south of the survey area, another zone of high resistance is thought to originate from a 1960’s excavation; however an archaeological interpretation cannot be wholly discounted.
The very high resistance values possibly originate from some form of hardcore that is shoring up the adjacent pavement and road. However, it is also feasible that this represents the former route of Little St. John Street. If that were the case, this may shed light on the linear low resistance anomaly adjacent to it that appears to be acting as a drain for groundwater. It may be that this is a drain running along the edge of the old road.
The primary features are related to current and former garden plans. A series of paths on the 1911 Ordnance Survey map have produced responses in the resistance. Some of these footpaths are still extant today but could not be surveyed by resistance.
An area of high resistance adjacent to the footpath may be significant as it suggests greater depth extent than the footpath, which is no more than a pair of trends in this latter data. The lack of discernable form to the anomaly and absence of a noticeable, coincident anomaly in the radar data would suggest that this is not archaeological.
The low resistance anomalies, cover a larger area in the deeper slices and thus may represent a pattern of water seepage through the ground.
It wasn't just the Amphitheatre itself that was surveyed, several places in the surrounding are were also included.
As you can see from the image (click for a much bigger gif file version (265Kb) to open in a new window) above quite a large area was surveyed in addition to the immediate Amphitheatre Site.
The areas in this version of the map are coloured in a pale yellow, and the main detail has been removed. This is because giving out such detailed information about unexcavated areas would put the archaeology at risk to unofficial and potentially damaging excavation.
However, details of what has been found in these areas is listed below.
The patterns of high and low resistance anomalies are most likely to represent a former, slightly altered, layout of the gardens.
Within the main body of the survey area there is a large high resistance zone whose interpretation remains uncertain. This also applies to other anomalies and the low resistance trends that ‘cut’ through these areas; whether they are a later feature or whether they are related remains open to debate.
To the north and west of the area there is a further pattern of high resistance anomalies that can be seen to have some rectilinear trends within their distribution, and possibly a loosely defined edge. While an archaeological interpretation is possible, given that this area is parkland and formal gardens, these responses are likely to be merely a facet of landscaping across the site.
The spread of low resistance anomalies also appear to be garden effects largely following the current footpaths (perhaps caused by run-off and subsequent ‘ponding’ of water within the soil adjacent to the paths) and surrounding trees and hedges.
This area lies at the bottom of the terracing along the southern edge of the park. Aside from the linear high resistance anomaly assumed to be a drain or service, it seems unlikely that the anomalies present are anything other than natural responses, probably related to the trees within the survey area.
The low resistance anomalies in this area are likely to represent natural groundwater distribution rather than any features of archaeological significance. The high resistance anomalies, after discounting what appear to be edge effects from the footpaths, have some rectilinear form and thus could possibly represent archaeological remains, however this interpretation is tentative.
The two small areas that made up the resistance survey in the northern grounds of the church have both show rectilinear high resistance anomalies. A tentative interpretation is that these are associated with the remains of the original church on the site; however they could also represent a former churchyard layout. The low resistance anomaly in the north-west survey area is likely to be an effect of a large tree.
This area of the church grounds is levelled, with a retaining wall surrounding it, thus the low resistance anomaly along the southwestern edges is likely to be water held up within the soil behind this wall. The pattern of high resistance anomalies, although patchy, is distinctly rectilinear and despite some concerns that this may have been an artefact of data collection, these have been tentatively interpreted as archaeological given their proximity to the current church and the remains of the previous church.
One anomaly is thought to be a garden feature and the high resistance anomalies in the east are probably associated with a row of trees.
The results from the resistance survey are largely inconclusive. The high resistance anomalies down each side of the survey area result from concrete pads to the east and light bases to the west. The high resistance anomaly to the south is the most interesting, but it is not possible to confidently draw any conclusions as to its origins given the confined nature of the response. The high resistance zone to the north may be related to earlier pipe kiln excavations.
Resistance survey over the amphitheatre site and environs has produced a large data set in which a number of anomalies have been identified that may be of archaeological significance. However, it has been difficult to interpret any of these as definitive evidence of further Roman remains.
The wider resistance survey has identified possible archaeological remains, believed to be of ecclesiastical origin, in the vicinity of St. John the Baptist’s church and a profusion of high resistance anomalies within Grosvenor Park. Although some of these anomalies are obviously garden features, questions remain over the interpretation of others, especially an expansive high resistance anomaly and surrounding responses in the south and east.
An anomalous high resistance feature within the garden of St. John’s Cottage has been classified as potentially being of archaeological significance.
Resistance survey was inconclusive in the Roman Gardens, however, a number of magnetic anomalies have been highlighted as significant responses. Although these could well be related to present day features, the discovery of a pipe kiln in the north of the survey area has meant that that an archaeological interpretation must be considered.
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