|
The following discussion forms part of the research design for the project in April 2002. The document draws heavily on the interpretation of the 2000 geophysical survey:
A geophysical survey of the site (Young 2000) revealed a complex of anomalies over an area of 3.5ha. The main part of the site is interpreted as an ironworks of mid C16 date, with three hand-blown bloomery furnaces on the terrace slopes and with a pond, fed by springs, supplying water to a water-powered forge on the floodplain below. The survey also extended over the adjacent low hill, and unexpectedly, showed evidence for a second cluster of furnaces on the crest of the hill, associated with a rectilinear ditched enclosure system and a scatter of Romano-British pottery in association with a spread of bloomery slag. Subsequent fieldwork has demonstrated that this scatter of slag apparently continues to the south of the M4 embankment over 300m to the south.
The investigation of the site forms a component of a long-term project into the history of iron-making around the outcrop of the iron oxide ores of Glamorgan border vale, which has included excavation of slag dumps associated with a Romano-British smelting site at School Lane, Miskin (Young & Macdonald 1999), together with a number of geophysical surveys, largely undertaken by TY with other staff funded by Cardiff Archaeology Section, as teaching exercises and undergraduate projects for both the Department of Earth Sciences and the Archaeology Section of Cardiff University. These include geophysical survey of the School Lane area (1997), geophysical survey of Mwyndy ironworks site (C16?) (1997), field survey of probable C16 iron-making site at Rhiwsaeson (1998), geophysical and geochemical study of a bloomery site in Cwmnofydd (1999) and geophysical survey of the Pont-y-parc mines (2001 and 2002).
The Caergwanaf uchaf site is exceptional for its apparent completeness and multi-period nature. Two aspects of the site have led to its research significance. Firstly, the earlier site on the hill top is of uncertain age. The scatter of pottery and the rectilinear ditches suggest a settlement of Roman age, although the wide area of iron-making and the apparently open nature of the settlement are quite unlike any other site of this age in Glamorgan. Local historians (Davies 2001) have tentatively suggested that Caergwanaf was an Early Medieval estate (partly on the basis of its being a curious detached portion of Talyvan lordship, which together with the two sections of Talygarn lordship and the manor of Llwynrhyddyd may have been parts of a larger Welsh lordship, later fragmented), and this settlement is the only early occupation site yet recognised within the area. Examination of the slags found on the surface suggests that they probably pre-thirteenth century, but they cannot be dated any more closely on the basis of current understanding of the technology. Carefully targeted small-scale excavation of representative components of the features indicated by the existing geophysical survey, together with future expansion of that survey, will aim to provide key dating evidence. The early iron industry of South Wales is very poorly known, and there is an almost complete lack of evidence for the nature of pre-medieval bloomery furnaces and technology. This site has the potential to provide significant new understanding.
The site is also important for the likely relationship of the lower part of the complex to the well-documented mid-C16 phase of exploitation of the resources of Clun Park. The documentary evidence includes an initial report of trial exploitation by Henry VIII in 1531/2 (PRO SP1/66/262), and a legal case concerning the lease of the mines during the 1540s (PRO C82/769, C66/697, C1/1062/1-3, C78/1/74). The report of the 1532 trials detail the operation of a hand-blown bloomery, with 3 concurrent blowers, and a daily production of two 1cwt blooms, from 3cwt of ore. These production figures are almost unique in their detail, and these general yield values have been substantiated by mass-balance investigation of slags from the nearby Mwyndy site (Thomas 2000; methodology of Thomas & Young 1999). In contrast to the documentary detail, the physical nature of such large, late, manually-blown bloomeries is completely unknown in Britain. Investigation of this technology has a particular currency because of the controversial ideas on bloomery operation being put forward by Sauder & Williams (Historical Metallurgy, forthcoming), who have demonstrated experimentally that extremely high blowing rates, believed outside the range of possible operating conditions by many European workers, can produce large high-quality blooms. Their operating conditions, batch time and yield are very close to those indicated in the 1532 report. Although several other bloomeries of this period are known or suspected within the district, no others have yet provided any evidence for survival of the bloomery furnaces themselves. At Caergwanaf the geophysical data suggest survival of furnace structures, although their situation on a steep slope, and the known levelling of the site in the 1950s, leaves their condition of preservation uncertain.
The Caergwanaf site has the potential to provide understanding of the changing technology of early iron-making, through providing evidence for iron-making at different periods, but employing the same natural raw materials. Such a case study would be of much greater significance for archaeometallurgy than the sum of the evidence from the two phases separately.
The aims of the 2002 excavations are threefold:
To further these aims up to four trenches are planned, depending on resourcing. In the upper, earlier, part of the site, trench 1 (5x5m) will be placed in an area over an anomaly interpreted as a furnace, with trenches 2 and 3 (3x6m) across enclosure ditches. Trench 4 (5x10m) will be on the terrace edge adjacent to one of the late bloomery furnaces, extending up slope to cover part of one of the geophysical anomalies which may be a building. The results of these trial investigations will enable appropriate decisions concerning site preservation and future research excavation.
