The Roman currency system included the denarius (plural: denarii), a small silver coin, as the most common coin in circulation.

First row : c. 157 BC Roman Republic, c. AD 73 Vespasian, c. 161 Marcus Aurelius, c. 194 Septimius Severus;
Second row: c. 199 Caracalla, c. 200 Julia Domna, c. 219 Elagabalus, c. 236 Maximinus Thrax

It is difficult to give even comparative values for money from before the 20th century, due to vastly different economies. Classical historians regularly say that in the late Roman Republic and early Roman Empire the daily wage for a laborer was one denarius.

The denarius was first struck in 211 BC during the Roman Republic, valued at 10 asses, giving the denarius its name which translates to "containing ten". In 118 BC it was re-tariffed at 16 asses, to reflect the decrease in size of the as. The denarius continued to be the main coin of the empire until it was replaced by the antoninianus in the middle of the 3rd century AD. The fineness of the silver content varied with political and economic circumstances.

Even after the denarius was no longer regularly issued, it continued to be used as an accounting device and the name was applied to later Roman coins in a way that is not understood. The lasting legacy of the denarius can be seen in the use of "d" as the abbreviation for the old French denier and the British penny prior to 1971. The denarius also survives in the common Arabic name for a currency unit, the dinar دينار, used from pre-Islamic times, and still used in several modern Arabic-speaking nations.

The gold aureus seems to have been a "currency of account", a denomination not commonly seen in daily transactions due to its high value. Numismatists think that the aureus was used to pay bonuses to the legions at the accession of new emperors. It was valued at 25 denarii.

1 gold aureus = 2 gold quinarii = 25 silver denarii = 50 silver quinarii =100 bronze sestertii = 200 bronze dupondii = 400 copper asses = 800 copper semisses = 1600 copper quadrans

See also: Roman currency, sestertius, dupondius, as, solidus and drachma.