The evolution of slave – owning resulted in the establish ment of a whole system of slave trading . Slave markets sprang up in Rome and in other regions . Foreign trade prevailed . Agricultural produce and luxuries were imported from the many Roman ” provinces ” ( conquered regions and dependent countries ) , while Rome exported metal implements , wine and olive oil . Imports were greater than exports . However , the lack of exports was compensated for by outright pillage of the conquered lands and , in particular , by the influx of large sums of money . By seizing the silver mines of Spain , Rome was provided with a permanent source of mint . The growth of commerce and money in circulation Created usurious capital . Companies of tax – farmers , the so – called publicans , were formed to carry out various operations involving credit and usury . Money – changers ‘ shops , sprang up everywhere . Their owners not only changed coins , but banked money , provided loans at an interest and remitted sums . Persons whose occupation was commerce and usury gradually formed a separate estate of the ruling class ,