Short answers, pulled from the story.
Roman currency was made from gold, silver, bronze, orichalcum (brass), and copper. In the early centuries, gold and silver coins had significant intrinsic value, while bronze coins served everyday transactions. Over time, the silver content of coins was progressively reduced through a process called debasement.
The denarius was introduced a few years before 211 BC and remained the backbone of the Roman economy until it ceased to be minted in significant quantities by the middle of the third century AD. When first issued, it contained nearly pure silver at a theoretical weight of approximately 4.5 grams.
The most common explanations for Roman coin debasement include a shortage of precious metals, inadequacies in state finances, and trade with India that drained silver from the Mediterranean world. War was also a major driver; raising armies and paying for supplies often required minting large quantities of coins with reduced silver content.
Diocletian reformed Roman coinage as part of his broader restructuring of the Empire, which also created the Tetrarchy (rule by four). The reform replaced the debased antoninianus with new denominations including an aureus struck at 60 to the pound, a new silver coin called the argenteus, and a large bronze coin containing two percent silver. In 301, he also issued an Edict on Maximum Prices, which ultimately could not be enforced.
Julius Caesar issued coins bearing his own portrait in 44 BC, making him only the third living individual in Roman history to appear on Roman coinage. The classicist Clare Rowan described this as often seen as a revolutionary moment in Roman history. The practice of featuring the living emperor's portrait became standard throughout the Imperial period.
The dinar descends from the Roman denarius via the Carolingian monetary system. The British pound and the peso both derive their names from the Roman libra, a unit of weight. Spanish dinero and Portuguese dinheiro, the common words for money in those languages, also trace back to the denarius. The word mint itself comes from the manufacture of silver coin near the temple of Juno Moneta in Rome in 269 BC.