The aureus was the ancient Roman gold coin introduced by Julius Caesar that became a major imperial currency.
Caesar introduced the aureus during his dictatorship in the first century BCE, helping establish a stable Roman gold denomination alongside the silver denarius. The coin was valuable and was primarily used for large payments, military finance and state transactions rather than everyday purchases.
Under Augustus, the aureus was standardized at 1/42 of a Roman pound of gold, or roughly 7.8 grams. Its weight and purity changed over later centuries, especially as emperors adjusted the monetary system to meet fiscal and military demands.
The aureus is often confused with the solidus. The solidus was introduced by Constantine the Great in the fourth century CE and eventually replaced the aureus as the principal Roman and Byzantine gold coin. The denarius, by contrast, was primarily a silver denomination.