The aureus was a Roman gold coin worth 25 denarii. It was first issued in the 1st century BC by Sulla  (138-78 BC) and remained until the 4th century (under Constantine the Great 307-337 AD) when it was replace by the Solidus.

Gold issues were rare until the civil war which erupted after the assasination of Julius Caesar. The coinage of Augustus eventually evolved into the first Roman Imperial coinage in gold.

The size and weight of the aureus was gradually reduced from about 8 grams at the time of Julius Caesar to 7.3g during the reign of Nero and eventually 6.5g by the reign of Caracalla. Interestingly however the purity of gold remained about the same at 99% pure. It therefore held it value well over time especially compared with the rampant debasement of the siver issues.

Some large issues such as the binio aureus (2 aurei) and quinarius (half an aureus) were also issued.