basic gold monetary unit of ancient Rome and the Roman world. It was first named nummus aureus (“gold money”), or denarius aureus, and was equal to 25 silver denarii; a denarius equaled 10 bronze asses. (In 89 BC, the sestertius, equal to one-quarter of a denarius, replaced the bronze ass as a unit of account.) In Constantine's reform of AD 312, the aureus was replaced by the solidus as the basic monetary unit.