The aureus

The aureus was a gold coin of ancient Rome originally valued at 25 pure 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 was about the same size as the denarius, but heavier due to the higher density of gold. Caesar began striking the coin more often, and standardized the weight at 1/40th of a Roman pound (about 8 grams).

This unique gold aureus of Augustus Caesar realized $781,675 U.S.

Augustus (29 BC – 14 AD) decreed the value of the sestertius as 1/100th of an aureus. The aureus was decreased to 1/45th of a pound (7.3 g) during the reign of Nero (54–68). After the reign of Marcus Aurelius (161–180) the weight fell to 1/50th of a pound (6.5 g).

The solidus was introduced by Diocletian (284–305) around 301 AD, struck at 60 to the Roman pound (5.5 g) and with an initial value equal to 1,000 denarii. The solidus was reintroduced by Constantine I (306–337) in 312 AD, permanently replacing the aureus as the gold coin of the Roman Empire. The solidus was struck at a rate of 72 to a Roman pound of pure gold, 4.5 grams of gold. Inflation was affected by the debasement of the silver denarius, which by the mid-3rd century had practically no silver left in it.

In 301, one gold aureus was worth 833 denarii; by 324, the same aureus was worth 4,350 denarii. In 337, after Constantine converted to the solidus, one solidus was worth 275,000 denarii and finally, by 356, one solidus was worth 4,600,000 denarii.
See ----->Decline of Roman Silver Coinage