RESOURCES

Many years of effort, not always successful, have been invested in locating the copper, tin and lead resources exploited in the Bronze Age and linking them with objects derived from those ores. Recently, for example, considerable excitement has been generated by the identification and dating of bronze age copper mines in Britain and Ireland. Similarly, the exploration and excavation of Roman mines has been a topic of research since work of Oliver Davies in the 1930s (Davies 1935). Possibly because interest has naturally been focused on the new metal, iron, there has been very little investigation of the non-ferrous metal resources used by Celtic smiths and, outside Britain, only a limited amount of scientific analysis of iron age copper alloy metallurgy. As yet no iron age copper mine has been found in Britain. However, there is good evidence for the exploitation of British copper and, probably, tin resources during the La Tene period and some of the earliest raw copper yet found on metalworking sites (Musson et al. 1993).

Although it makes good sense to assume that British copper ores were being mined and smelted during the Late Bronze Age, there is no direct evidence. The copper ingots, common in the ninth-eighth centuries BC in southern and eastern England, appear to have been exported from the Continent, although a few may come from the south-west, where there is also a limited distribution. A dependence on scrap bronze from the Continent, and also from Ireland, is also evident. For the seventh-sixth centuries there are even fewer clues and it is quite possible that by the end of the sixth century BC copper and tin extraction had virtually ceased in Britain. Lead mining probably stopped even earlier as the alloys of this period are mainly lead-free.

Even in the earliest La Tene period there were the beginnings of a revival in metallurgical activity and new, previously unused copper deposits were opened up. The best example of this is in the area of the Llanymynech hill-fort and the Tanat valley, just on the Welsh side of the Powys/Shropshire border. Two hearths excavated on the hill-fort ramparts date to the second/first centuries BC and were used for processing a zinc - and lead-rich copper. The hill-fort itself stands over a copper mine which could have supplied the right ore to produce this metal, a mine, moreover, that is believed to have been exploited in Roman times. The same raw copper and associated slag have been excavated from a metallurgical context at the small hill-fort of Llwyn Bryn-dinas in the Tanat valley with a C-14 date that takes the use of this metal back at least to third century BC, perhaps even further. Together with other excavated material and the analysis of bronze objects it is possible to demonstrate the existence of a copper extraction industry based on the ores of this area, with products mainly distributed in north and east Wales, although examples are known from as far away as Llyn Cerrig Bach in Anglesey (Northover, 1991a; Musson et al. 1993). It appears that the source was not used before the fifth-fourth centuries, and it may have come to an end in the first century BC.

The same chronology applies to a second source for which the evidence is rather more circumstantial. A large quantity of bronze has now been analysed, with a very characteristic impurity pattern in which arsenic, cobalt and iron are the most important elements; where nickel is present there is always more cobalt than nickel. This metal is most common in southern and south-western England and on several sites, for example Maiden Castle hill-fort (Northover 1991b), all the metalworking waste is of this composition. The distribution of this metal hints at a source in the south-west and there is some confirmation from analyses of bronze age metalwork. In about the fourteenth century BC there Is a type of bronze axe specific to Devon and Cornwall and those examples clustered around Dartmoor have the same arsenic/cobalt/iron impurity pattern (Northover unpublished). A source in this area also has the benefit of being close to major tin sources. There has always been speculation about the exploitation of the mineral wealth of Devon and Cornwall in prehistory. Both tin and copper were certainly produced there In the Bronze Age, but it is impossible to gauge how much was mined. An industry of significant size in that region seems to be a creation of the Iron Age so it can be argued that classical writers did actually have knowledge of a real Industry that was in a position to export both tin and bronze. There Is a long way to go In testing the evidence but it may well be more than coincidence that the sheet bronze In the cauldrons found at La Tene itself are made of the same type of bronze. It is also noteworthy that the same Impurity pattern appears in both the earliest cast bronze Celtic coins made in Britain and their Massiliote prototypes (Northover 1992).

These are two of the best characterized metal types In the British Iron Age. There are several others and some at least must represent imported metal coming from either the Continent or Ireland. We have seen that there was a change in the utilization of metal resources at the beginning of the La Tene period. The demise of the two metal groups detailed above In the mid-first century BC and the increasing importance of others shows that further major changes occurred at that time. It Is tempting to associate them with the events of, or consequent upon, either supposed Belgic migrations to Britain, or the Roman occupation of Gaul and the Romans’ first incursions into Britain but it is impossible to be that precise in the dating of any site or artefact. Both literary evidence and events after the conquest show that the Romans were interested In British resources, so it is curious that what appear to have been flourishing British mines were abandoned when they were. It is, of course, possible that the decline was caused by the British market being invaded by the potential surplus of metal brought into Gaul by the Romans and then increased by the occupation.