Roman coins were minted in bronze, silver and gold. Throughout the years, the values of coins have fluctuated with inflation and intentional debasing. Emperors sometimes instituted new denominations of coins, while others were replaced or simply fell out of circulation. The base bronze coin was the As, the base silver coin was the Sestertius and the base gold coin was the Aureus. These coins formed the standard from which the values of other coins were calculated.
According to Zander H. Klawans, coins called the aes grave (heavy bronze) began appearing around the year 300 BCE. The denominations of all early bronze coins contained the prow of a ship on the reverse. The obverse (front) had depictions of gods. The as depicted Janus; the semis, Jupiter; the triens, Minerva; the quadrans, Hercules; the sextans, Mercury; the uncia, Roma.
As: The base bronze coin
Semis: worth 1/2 an as Triens: worth 1/2 of an as Quadrans: worth 1/4 of an as Sextans: worth 1/6 of an as Uncia: worth 1/12 of an as Dupondius: worth two asses Tripondius: worth three asses Quadrussis: worth four asses Quincussis: worth five asses Decussis: worth 10 asses Follis: introduced by Emperor Diocletian; bronze with a silver wash Centenionalis: introduced by Emperor Constantine I; bronze with a silver wash
Francesco Gnecchi states that the first silver coins were struck in 268 BCE. They depicted the goddess Minerva on the obverse and Castor and Pollux (the Dioscuri) with the word Roma on the reverse. Later they depicted the emperors.
Sestertius: the base silver coin; worth 2 1/2 asses Quinarius: worth two sestertii Victoriatus: originally used to replace foreign coinage; later worth two sestertii Denarius: worth four sestertii Antoninianus: introduced by Emperor Caracalla; worth eight sestertii Siliqua: introduced by Emperor Constantine I; worth 1/24 of a solidus
Miliarensis: introduced by Emperor Constantine I; worth 1/14 of a solidus
According to Gnecchi, the first gold coins were struck in 217 BCE. They depicted the god Mars on the obverse and an eagle with the word Roma on the reverse. Later they contained portraits of emperors.
Aureus: the base gold coin; originally worth 20 denarii Quinarius: cast in silver and gold; both worth two sestertii Solidus: introduced by Constantine I to replace the aureus; worth one denarius Semis: worth 1/2denarius or 1/2 solidus Triens: worth 1/3 denarius