The gold solidus had a run for nearly 700 years.
the silver denarius was a problem, as it was the common coin. It was adulterated down to pretty much zero silver content at one point.
From wikipedia FWIW
https://en.wikipedia.org/wiki/Roman_currency
Although the denarius remained the backbone of the Roman economy from its introduction in 211 BC until it ceased to be normally minted in the middle of the third century, the purity and weight of the coin slowly, but inexorably, decreased. The problem of debasement in the Roman economy appears to be pervasive, although the severity of the debasement often paralleled the strength or weakness of the Empire. While it is not clear why debasement was such a common occurrence for the Romans, it’s believed that it was caused by several factors, including a lack of precious metals and inadequacies in state finances. When introduced, the denarius contained nearly pure silver at a theoretical weight of approximately 4.5 grams.
The theoretical standard, although not usually met in practice, remained fairly stable throughout the Republic, with the notable exception of times of war. The large number of coins required to raise an army and pay for supplies often necessitated the debasement of the coinage. An example of this is the denarii that were struck by Mark Antony to pay his army during his battles against Octavian. These coins, slightly smaller in diameter than a normal denarius, were made of noticeably debased silver. The obverse features a galley and the name Antony, while the reverse features the name of the particular legion that each issue was intended for (it is interesting to note that hoard evidence shows that these coins remained in circulation over 200 years after they were minted, due to their lower silver content). The coinage of the Julio-Claudians remained stable at 4 grams of silver, until the debasement of Nero in 64, when the silver content was reduced to 3.8 grams, perhaps due to the cost of rebuilding the city after fire consumed a considerable portion of Rome.
The denarius continued to decline slowly in purity, with a notable reduction instituted by Septimius Severus. This was followed by the introduction of a double denarius piece, differentiated from the denarius by the radiate crown worn by the emperor. The coin is commonly called the antoninianus by numismatists after the emperor Caracalla, who introduced the coin in early in 215. Although nominally valued at two denarii, the antoninianus never contained more than 1.6 times the amount of silver of the denarius. The profit of minting a coin valued at two denarii, but weighing only about one and a half times as much is obvious;