From the end of the 1st Century BC until the middle of the 3rd Century, the Roman monetary system consisted of a number of denominations made from four different types of metal: gold, silver, orichalcum (a kind of brass) and copper.

The Emperor Augustus(31BC to 14AD) standardised the coinage that was minted into seven denominations, aureus(gold), denarius(silver), sestertius(orichalcum), dupondius(orichalcum), as (copper), semis(copper or orichalcum) and quadrans(copper). (see below)

Name	Metal	Values
quadrans	copper	quarter of an as
semis	copper or orichalcum	half an as or two quadrantes
as	copper	4 quadrantes
dupondius	orichalcum	2 asses
sestertius	orichalcum	4 asses or 2 dupondii
denarius	silver	16 asses, 8 dupondii or 4 sestertii
aureus	gold	400 asses, 200 dupondii, 100 sestertii or 25 denarii

During the first 200 years of the Roman Empire there was little change in this system, except that the silver content of the denarius was progressively reduced from the time of the Emperor Nero onwards (A.D.54-68) and was accompanied by a series of downward adjustments in the weight of the gold coins (but they were still struck pure).

In the later empire new denominations were added by, the Emperor Caracalla (211-217 AD) who introduced the silver antonianus (worth two denarii); Diocletian (284-305 AD) who replaced this with the bronze follis, and Constantine (306-337 AD) introduced the gold solidus.

The gold aureus, first introduced during the Second Punic War, became more widely used, although the as and denarius remained in circulation. Typically, gold and silver coins had official use, such as the paying of salaries, while the brass and bronze coins were used in everyday transactions.

Responsibility for minting coins lay with the Senate, in the hands of junior magistrates called Tresviri Monetales During the Empire minting took place in several different cities. The emperor had sole responsibility for minting gold and silver coins, while brass and copper coin mints were located throughout several provinces.