Mining and Metallurgy

The main mining regions of the Empire were Spain (gold, silver, copper, tin, lead); Gaul (gold, silver, iron); Britain (mainly iron, lead, tin), the Danubian provinces (gold, iron); Macedonia and Thrace (gold, silver); and Asia Minor (gold, silver, iron, tin). Intensive large-scale mining—of alluvial deposits and by means of open-cast mining and underground mining—took place from the reign of Augustus up to the early 3rd century CE, when the instability of the Empire disrupted production. The gold mines of Dacia, for instance, were no longer available for Roman exploitation after the province was surrendered in 271. Mining seems to have resumed to some extent during the 4th century.

Hydraulic mining, which Pliny referred to as ruina montium ("ruin of the mountains"), allowed base and precious metals to be extracted on a proto-industrial scale. The total annual iron output is estimated at 82,500 tonnes. Copper was produced at an annual rate of 15,000 t, and lead at 80,000 t, both production levels unmatched until the Industrial Revolution; Spain alone had a 40 percent share in world lead production. The high lead output was a by-product of extensive silver mining which reached 200 t per annum. At its peak around the mid-2nd century AD, the Roman silver stock is estimated at 10,000 t, five to ten times larger than the combined silver mass of medieval Europe and the Caliphate around 800 CE. As an indication of the scale of Roman metal production, lead pollution in the Greenland ice sheet quadrupled over its prehistoric levels during the Imperial era, and dropped again thereafter.

The invention and widespread application of hydraulic mining, namely hushing and ground-sluicing, aided by the ability of the Romans to plan and execute mining operations on a large scale, allowed various base and precious metals to be extracted on a proto-industrial scale only rarely, if ever, matched until the Industrial Revolution. The most common fuel by far for smelting and forging operations, as well as heating purposes, was wood and particularly charcoal, which is nearly twice as efficient. In addition, coal was mined in some regions to a fairly large extent: Almost all major coalfields in Roman Britain were exploited by the late 2nd century CE, and a lively trade along the English North Sea coast developed, which extended to the continental Rhineland, where bituminous coal was already used for the smelting of iron ore.