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One of the more tangible benefits that accrued to Rome from the conquest of an empire was the acquisition of significant mineral resources, significant because Italy, although rich in iron, could not provide a sufficient supply of the whole range of metals needed by the Roman state for coinage and by members of the elite for the luxury artefacts that helped to enhance their social status. Once Rome had gained control over metalliferous regions of the Mediterranean, Romans, and especially Italians, were not slow to become involved in mining overseas, while the state came to gain considerable revenue from the leasing of contracts for the right to exploit state-owned mineral resources. Recent archaeological work has done much to improve our understanding of the techniques of mining and processing of raw metals, while the study of ingots (found mainly in shipwrecks) has allowed some insight to be gained not only into ways in which metals were transported, but especially into the modes of administrative control of metal production. Interest in general has centred on mining in the late Republic and early Empire; very little attention has been paid to its later history during either the later Roman Empire or the early medieval period. Yet the need for metals of all types was just as, if not more, pressing during the late Empire. At all times iron remained the metal most in demand—for arms and armour, constructional and agricultural tools, and building materials such as nails, hinges, and fittings. Fortunately it was found in many parts of the Empire, usually in sufficient quantities to allow something approaching regional self-sufficiency. There were some large-scale iron-mining districts (for example, the Kentish Weald or, still more, in Noricum); these produced a considerable surplus to supply the Roman army. But more typically, iron was exploited on a much smaller scale, sometimes even at a domestic level of production. Since its supply was rarely problematic, iron will largely be excluded from the following discussion. Attention instead will focus on the precious metals, gold and silver, and, to a lesser extent, on copper and tin. These metals could only be obtained in certain regions of the Empire, and so greater official concern over their supply and closer central control over their production were necessary.