NGC Ancients: Coin Denominations of the Roman Empire

This month we'll survey coin denominations used in the Roman Empire from the accession of Augustus in 27 B.C. to the loss of Roman territories in Europe in A.D. 476. Only the main denominations will be discussed, though there were various fractions and multiples. In addition to the “imperial” coinages, there was a bewildering variety of provincial coins struck to local standards.

The Roman coinage system underwent constant adjustments and reforms, and if observed over the long course of history it is a mirror to the rise and fall of Rome’s fortunes. There was a steady decline in the intrinsic value of Roman coins, which rebounded only briefly in moments of reform that were well-intended but typically ineffective.

The core denominations in the early empire were the copper “as”, the silver denarius and the gold aureus. The as had been a fundamental unit since the earliest days of Republican coinage and was in regular use for more than 500 years. During imperial times it was struck in great quantity along with its sister-denominations, the brass dupondius (worth two asses) and the brass sestertius (four asses). Over time the composition of dupondii and sestertii was degraded, and they lost their golden-color.

The empire’s main precious metal coins were the silver denarius and gold aureus; both were struck in tremendous quantities and were the backbone of the Roman monetary system. Denarii must have been popular for larger daily transactions, and almost certainly were a common medium for the payment of wages. Gold aurei were of significantly greater value and would have been used only for high-level transactions.

The structure of this money system was virtually unchanged for nearly 250 years, despite being subject to reductions in weight and composition. In A.D. 214 or 215 the Emperor Caracalla (A.D. 198–217) introduced an important new denomination: the double-denarius. Colloquially known today as an antoninianus, it was about 1.5 times the weight of a denarius but seems to have been intended as a double. By about A.D. 241 it had replaced the denarius.

As Rome's fortunes plummeted, so did the integrity of its coinage. For example, by the 260s the weight of the gold aureus had become inconsistent and sometimes extremely low. Furthermore, the purity of the double-denarius — by then struck on ragged, irregular planchets — had dropped to less than two percent, and the major copper denominations ceased to be issued regularly.

The emperor Aurelian (A.D. 270–275) attempted to reform the increasingly worthless coinage, mainly by introducing a coin that contained five percent silver. This coin often is thought to be an upgraded double-denarius, but it is in fact an entirely new denomination that scholars call an aurelianianus. This attractive coin survived about thirty years.

Denominations in the late empire are more complex than those of earlier times, and the relational values are often a complete mystery. This is mainly because inflation was out of control and even the best laid plans for coin values could become obsolete in a short period of time.

Another great coinage reformer, Diocletian (A.D. 284–305), is best known for his reforms in other areas, including provincial administration, taxation and the military. His naive attempt to control inflation by dictating maximum prices on a wide range of goods and services was a dismal failure, and only caused prices to spiral even further out of control.

In an effort to tame the economy, Diocletian reformed the coinage by scrapping all of the old denominations except the gold aureus. He introduced a high-purity silver coin that is known today as an argenteus, and a large and heavy copper coin alloyed with a small amount of silver that often is called a follis, but is more correctly termed a nummus.

The argenteus was a dismal failure because it was such a good coin: it rarely circulated since it left the empire via trade or was hoarded. The nummus found regular use, though its weight and purity continually declined until it was less than one-third of its initial weight and had virtually no silver.

Constantine I “the Great” (A.D. 307–337) was the next important coinage reformer, whose most significant contribution was the introduction of a lighter gold coin, commonly known as a solidus. By A.D. 324 this coin had replaced the aureus. At 1/72nd of a pound, it set the standard for centuries beyond the collapse of the Western Roman Empire. A one-third solidus, called a tremissis, also became an important coin in its own right.

Coins of good silver were also introduced by Constantine. The principal denomination, today called a siliqua, was the same weight and purity as the argenteus, but was struck on a broader, thinner planchet. Why it succeeded when Diocletian's argenteus had failed is a mystery. Some three decades after it had been introduced, the weight of the siliqua was reduced and afterward was cut further still.

The base metal and billon coins of the late period were the most susceptible to the ravages of inflation, and Constantine could do little to reform them except to manage their decline with continuous reductions in their intrinsic value.

Production of the nummus halted in about A.D. 318 or 319, by which time it was a reduced version of Diocletian’s original coin. It was replaced by a more compact coin that is usually called an “AE3” by numismatists. Even this coin eventually shrank to the “AE3/4” size, and then the “AE4” size. The smallest version of this coin continued to be struck in ever-smaller versions until the beginning of the Byzantine age.

Larger bronze and billon coins were also struck at various times from the mid-4th Century onward, including one type commonly called a centenionalis. Others are described in the formulaic manner, such as “AE2” or “AE1,” to categorize them by size. These, like the AE3s and AE3/4s typically have a trace of silver in their alloy, and often had a thin layer of “silvering” on the surface.

As this general survey shows, assembling a set of Roman coins based on denomination would be both interesting and educational, and would allow any collector to learn a great deal about the rise and the fall of the Roman Empire.