This article appeared in the Winter 1973 (Issue #34) edition of the Kent Archaeological Review.
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Iron-working in Roman Britain.
Britain has been a major iron-making country throughout historical times and in fact during the Roman occupation it was one of the most important iron producers of the Roman Empire. Iron-working had started in the Weald of Kent and Sussex in the last century before Christ and therefore pre-dated the Roman invasion by some 70 years.
The Caucasus region boasts the discovery of iron-smelting and from here, the knowledge of this new technique spread throughout the Old World. The use of iron reached the basin of the Upper Danube by approximately 900 BC and from this area it was carried by the migrating Celts westwards into France and the Iberian peninsular and north-west across Germany to the British Isles.
By Roman times nearly all the major iron ore deposits in Britain were being worked, including the haematites of Cumberland and the coal measures' Blackband ores. In addition, the carstones of East Anglia were exploited, a then important source of iron which is now of so little significance that most authors fail even to mention it. By this period, the most distinct iron regions of the country had begun to appear; namely the Weald and the Forest of Dean and it is of interest to note that these two areas remained supreme until the Industrial Revolution and the introduction of coke for smelting. In marked contrast to the present location factors of the industry, in the first century AD, economic conditions were ideal here, away from coal-fields, as the ore was very easily reduced in the primitive furnaces, while charcoal supplied the fuel from the abundant reserves in the surrounding forest areas.
As the ore-bearing strata were found at or near the surface, mining was simple to undertake by the open-cast method and today the Weald contains the remains of many ore-pits, most of which are datable to the Roman period. The only evidence so far available to show that ore was at all mined underground is provided by Sir Mortimer Wheeler's 1928-9 excavation at Lydney Park in Gloucestershire, where there was no organised shaft or tunnel system, but ore production seemed, nevertheless, substantial.
Smelting was carried on in a variety of furnace types. It was a simple process in which small pieces of ore and twice as much charcoal, were heated on a hearth and the temperature was raised by a strong draught. The hearths were generally built of clay or perhaps of stone, in which case they had a clay lining. At first the wind was funnelled onto the hearth, as can be seen in the diagram of the furnace at Ashwicken in Norfolk, and then a bellows, worked by the strength of either man or animal, was used. An example of this type of furnace has been found at Holbeanwood in the Sussex Weald.
In its combustion, the charcoal fuel combined with the oxygen in the ore to form carbon dioxide. As pure iron melts at 1537°C, and Roman bloomeries were unlikely to achieve such high temperatures, the reduced iron could never have been molten. Instead it would have become a semi-plastic, pasty mass containing much slag due to the partial fusing of foreign matter within the iron, which could be shaped by hammering. The liquid form of pig-iron was not known until much later when higher temperatures were attained in the hearths.
The iron which emerged had rarely absorbed much carbon, and as the metal had never reached a fluid state, the particles of slag and unreduced ore had never separated from the iron. The resulting substance was uneven in texture and quality, but apart from this deficiency the metal was, in effect, pure iron.
The spongy bloom was removed from the hearth and then repeatedly heated and hammered in an attempt to reduce the amount of slag and thus to consolidate the metal. The end product was soft and could be bent and fashioned easily, but would not take a sharp cutting edge. It could be welded, but its strength was very limited.
From the Weald, which had a very elaborate road system, iron would have men distributed to the towns of the South-East, including Canterbury, Winchester and London. The Weald has yielded evidence of at least six Roman iron-working sites, most of which seem to have been in operation for about 200 years and the amount of slag was of the order of tens of thousands of tons. It is estimated that at Beaufort Park near Hastings, the original slag heap must have contained well over 50,000 tons of waste material, inferring that at least 25,000 tons of iron were produced in quantities of about 3-4 <lbs per blast.
With the Forest of Dean presumably producing roughly the same amount of iron as the Weald, the supply must have far exceeded the Romano-British demand and consumption. One may therefore conclude that Britain was a major exporter of iron during the first few centuries of the Christian era and sent shipments possibly to Gaul and Spain. Germany had its own bloomeries in the Siegerland.
Little is known about the Roman organisation of the iron-working industry. In Gaul, the metal seems to have been exploited by limited companies under Imperial letters patent, but Cleere maintains that he has found evidence for indirect State operation in Britain due to the CLBR stamped tiles discovered at Bardown and Beaufort Park, which were also iron smelting centres. The argument put forward is that as the mid-Roman occupation was a period of relative stability, the British Fleet may have had a quasi-commercial role, making iron in large industrial settlements and exporting it throughout the western provinces. Evidence of iron-working at Dover would lend much weight to this hypothesis, which otherwise must await future excavation of Wealden bloomeries, as "the organisation of Roman iron-working in Britain is still lost in obscurity." (Stamp).
(Much of this article is based on the work of Henry F Cleere.)