The aureus (pl. aurei) was a gold coin of ancient Rome valued at 25 silver denarii. The aureus was regularly issued from the 1st century BC to the beginning of the 4th century AD, when it was replaced by the solidus. The aureus is approximately the same size as the denarius, but is heavier due to the higher density of gold.
Before the time of Julius Caesar the aureus was struck very infrequently, usually to make large payments from captured booty. Caesar struck the coin more frequently and standardized the weight at 1/40th of a Roman pound (about 8 grams). The mass of the aureus was decreased to 1/45th of a pound during the reign of Nero.
After the reign of Marcus Aurelius the production of aureus decreased, and the weight was further decreased to 1/50th of a pound by the time of Caracalla. During the third century gold pieces were introduced in a variety of fractions and multiples making it hard to determine the intended denomination of a gold coin.
Constantine introduced the solidus in 309. replacing the aureus as the standard gold coin of the Roman empire. The solidus was a larger diameter and flatter coin, while the aureus was smaller and chunky and similar to the denarius in fabric.
See also: Roman currency
