Coins of ancient Rome generally fall into two categories—those struck during the Roman Republic, which lasted from 509 until 27 BCE, and coins minted during the Roman Empire, which ran its course in the West at the end of the 5th century.
The earliest coins of the Republican era were cast in irregular bronze shapes and exchanged based on their weight, hence their name aes (latin for bronze) rude. The aes signatum coins of the 3rd century BCE were also weight-based coins, although they featured depictions of animals (cattle were common) and symbols such as shields.
The heavy bronze, or aes grave, coins appeared around 289 BCE. Though still cast, the coins were circular and came in numerous denominations. A coin called the as featured the twin-head of Janus on its obverse, while the quadran showcased Hercules.
By the time of the Empire, Roman coins were being struck in gold and silver, as well as copper and brass. Probably the most common Empire coin was the denarius, although the aureus may be the best known since it featured Caesar on its face. Other common coins bore the likenesses of emperors Trajan, under whose rule Rome reached its greatest extent, and Hadrian.