<P> A professional deposit banker (argentarius, coactor argentarius, or later nummularius) received and held deposits for a fixed or indefinite term, and lent money to third parties . The senatorial elite were involved heavily in private lending, both as creditors and borrowers, making loans from their personal fortunes on the basis of social connections . The holder of a debt could use it as a means of payment by transferring it to another party, without cash changing hands . Although it has sometimes been thought that ancient Rome lacked "paper" or documentary transactions, the system of banks throughout the Empire also permitted the exchange of very large sums without the physical transfer of coins, in part because of the risks of moving large amounts of cash, particularly by sea . Only one serious credit shortage is known to have occurred in the early Empire, a credit crisis in 33 AD that put a number of senators at risk; the central government rescued the market through a loan of 100 million HS made by the emperor Tiberius to the banks (mensae). Generally, available capital exceeded the amount needed by borrowers . The central government itself did not borrow money, and without public debt had to fund deficits from cash reserves . </P> <P> Emperors of the Antonine and Severan dynasties overall debased the currency, particularly the denarius, under the pressures of meeting military payrolls . Sudden inflation during the reign of Commodus damaged the credit market . In the mid-200s, the supply of specie contracted sharply . Conditions during the Crisis of the Third Century--such as reductions in long - distance trade, disruption of mining operations, and the physical transfer of gold coinage outside the empire by invading enemies--greatly diminished the money supply and the banking sector by the year 300 . Although Roman coinage had long been fiat money or fiduciary currency, general economic anxieties came to a head under Aurelian, and bankers lost confidence in coins legitimately issued by the central government . Despite Diocletian's introduction of the gold solidus and monetary reforms, the credit market of the Empire never recovered its former robustness . </P> <P> The main mining regions of the Empire were the Iberian Peninsula (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 AD, 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 . </P> <P> 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; Hispania alone had a 40% 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 AD . 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 . </P>

When did rome become a de facto empire