used before explosives became common. It involved building a fire against a hard rock face, then quenching the hot rock with water, so that the thermal shock cracked the rock and allowed the minerals to be extracted. The method is described by Diodorus Siculus when he discussed the gold mines of Ancient Egypt in the first century BC, and at a much later date by Georg Agricola in his De Re Metallica of the 16th century. Every attempt was made to ventilate the deep mines, by driving many long adits for example, so as to ensure adequate air circulation. The same adits also served to drain the workings. Fall of the metal economy The Roman economy depended on the abundant metals that were mined in many regions. Approximately 100,000 tons of lead and 15,000 tons of copper were sourced within the imperial territory and about 2,250 tons of iron were produced each year. This abundance and extensive production of metal contributed to the pollution in Greenland ice, and it also affected the metal industry as more and more inexpensive metals were available throughout the empire. The production and availability of smelted metal started to cease during the late fourth century as the Romano-British economy began to decline. The only solution for people who needed metals as part of their livelihood was to scavenge for metal scraps. This is evident from the excavated metalworks from Southwark and Ickham. By the end of fourth century Britain was unable to sustain the need for metals, and so many metal-working sites were abandoned and skilled workers left with no jobs. See also Mining in ancient Rome Derbyshire lead mining history Dolaucothi Gold Mines Metal mining in Wales Roman engineering Roman technology Roman metallurgy Notes References Davies, O, Roman Mines in Europe, Oxford (1935). Elkington H.D.H.The Mendip Lead Industry in Branigan K. and Fowler P.J. The Roman West Country (1976) Elkington H.D.H. The Development of the Mining of Lead in the Iberian Peninsula and Britain under the Roman Empire. Durham University Library (1968) Jones G. D. B., I. J. Blakey, and E. C. F. MacPherson, Dolaucothi: the Roman aqueduct, Bulletin of the Board of Celtic Studies 19 (1960): 71-84 and plates III-V. Lewis, P. R. and G. D. B. Jones, The Dolaucothi gold mines, I: the surface evidence, The Antiquaries Journal, 49, no. 2 (1969): 244-72. Lewis, P. R. and G. D. B. Jones, Roman