Individual Roman Bronze Coins

Following the currency reforms of Augustus in 23 BC, the As was struck in reddish pure copper (instead of bronze), and the sestertius or 'two-and-a-halfer' (originally 2.5 asses, but now four asses) and the dupondius (2 asses) were produced in a golden-colored alloy of bronze known by numismatists as orichalcum. The as continued to be produced until the 3rd century AD. It was the lowest valued coin regularly issued during the Roman Empire, with semis and quadrans being produced infrequently, and then not at all sometime after the reign of Marcus Aurelius. The last as seems to have been produced by Aurelian between 270 and 275 and at the beginning of the reign of Diocletian.

During the early Roman Empire, several bronze coin types were in circulation, each with its distinct characteristics and denominations:

Sestertius: The largest and heaviest bronze coin. The name sestertius means "two and one half", referring to its nominal value of two and a half asses, a value that was useful for commerce because it was one quarter of a denarius, a coin worth ten asses. The name is derived from semis, "half" and "tertius", "third", in which "third" refers to the third as: the sestertius was worth two full asses and half of a third. Later, the sestertius was re-values to 4 Asses. 

As: One quarter of a sestertius is equal to a medium bronze coin called an As. This bronze coin was the lowest form of currency found outside Rome. You couldn't buy much with an As coin except maybe a cup of cheap wine.

Semis: The Semis was worth half of an As and was smaller and lighter than both the As and Sestertius. It typically portrayed the emperor's head on the obverse and various symbols on the reverse. Semis coins were used for smaller transactions and were less frequently encountered than the larger denominations.

Dupondius: The Dupondius was worth two As or twice the value of a Sestertius. It featured the emperor's portrait, usually with a radiate crown, on the obverse and diverse designs on the reverse. Dupondii were larger than Semis coins but smaller than Sestertii. They were less common in circulation and served as a higher-value denomination.

These bronze coins were essential in the Roman economy, representing the power and authority of the emperor and facilitating various transactions throughout the empire.