Roman Imperial Coinage: Five Centuries of Caesar's Money

The empire behind the coin

Roman Imperial coinage is the money struck under the emperors, from the settlement of 27 BC that made Octavian into Augustus down to the deposition of the boy Romulus Augustulus in AD 476. That is five centuries of continuous state coinage — nothing else in the ancient world comes close for sheer volume or for how completely it has been catalogued. The standard reference, RIC (Roman Imperial Coinage), runs to ten volumes; it was begun by Harold Mattingly and Edward Sydenham in 1923 and revised over the following seventy years.

Three structural eras organise the whole series. The Principate (27 BC to about AD 235) is the long stable period of the Julio-Claudians through the Severans. The Crisis of the Third Century (about 235 to 284) is fifty years of usurpation, invasion, and currency collapse. The Dominate, or Late Empire (284 to 476), opens with Diocletian's rebuilding and runs to the end in the West. The coinage tracks all of it. Augustan moral legislation, Trajan's Dacian wars, Hadrian's tour of the provinces, Constantine's Christogram — each shows up as a reverse type, because the coin was the empire's mass medium long before anything else could do that job.

One consequence matters for collectors: minting decentralised over time. Under Augustus the precious metal came largely from Lugdunum; by the fourth century a network of regional imperial mints — Trier, Siscia, Thessalonica, Antioch, Constantinople — was striking the same types in parallel, each marked in the exergue. Reading that mint mark is most of late-Roman attribution.

How the money worked

The Augustan system is the baseline everything else is measured against: one gold aureus equalled 25 silver denarii, equalled 100 brass sestertii, equalled 400 copper asses, with the dupondius worth two asses and the semis and quadrans below the as. The aureus weighed around 7.8 grams of fine gold. The denarius, near-pure silver at roughly 3.9 grams, was the structural unit — it was what a legionary's pay was reckoned in and what a market price was quoted in.

Then it eroded, and the coinage records the erosion with unusual precision. Nero's reform of AD 64 trimmed the aureus and the denarius and quietly lowered the denarius's silver content. That is the hinge. Every later debasement followed the path Nero opened. By the Severan period the denarius was under half silver; Caracalla responded in AD 215 with the antoninianus, a radiate-crowned coin tariffed at two denarii but containing only about one and a half denarii of silver. It was a fiscal sleight of hand, and the third century paid for it: by the 270s the antoninianus was a silver-washed copper token.

Aurelian tried to stop the slide in AD 274 with a retariffed coin marked XXI (or KA in the Greek-using East), a guarantee of a 20-to-1 base-to-silver ratio. It bought time, not a cure. The real reset came under Diocletian. His reform of AD 294 swept away the exhausted system and introduced a new structure: gold aureus, a revived good-silver argenteus, and a large silvered-bronze nummus — the coin collectors call the follis. Constantine finished the job. Around AD 309 he introduced the gold solidus at 1/72 of a Roman pound, roughly 4.5 grams, struck to a standard so stable it outlived the Western Empire by seven hundred years and carried straight into Byzantine coinage.

Two attribution habits are worth fixing early. First, the brass and copper of the Principate carries the letters SC — Senatus Consulto, "by decree of the Senate" — a constitutional fiction that the Senate ran the base-metal coinage while the emperor controlled gold and silver. No SC, and you are usually not looking at an imperial bronze of that period. Second, the imperial series is not the only Roman money a collector meets: the Greek-speaking East kept striking its own civic and provincial coinage under the same emperors, on different standards and in Greek, well into the third century. Those belong to Roman Provincial coinage, catalogued in RPC rather than RIC, and a portrait of Hadrian on a billon tetradrachm of Alexandria is a provincial coin, not an imperial one.

The denominations

A working vocabulary, gold down to copper. Each links to its catalogued inventory.

Denomination	Metal	What to know
Aureus	Gold	High-value gold of the Principate, around 7.8 g under Augustus, trimmed repeatedly after.
Solidus	Gold	Constantine's replacement, ~4.5 g, the reserve money of late antiquity.
Denarius	Silver	The workhorse for three centuries — wages and prices. Deeper: Roman denarius.
Antoninianus	Silver / billon	Caracalla's radiate double-denarius. Tell it from a denarius by the radiate crown.
Sestertius	Orichalcum	Roughly 25 to 28 g — the finest canvas Roman engravers ever had.
Dupondius & as	Brass / copper	Daily money; the emperor's radiate crown marks a dupondius, laureate an as.

One naming trap worth stating plainly: the late bronze every dealer calls a "follis" is usually listed in RIC by its modern size class — AE2, AE3, AE4 — not by an ancient name. Search the catalogue by size if the denomination term comes up empty.

By dynasty

The imperial series is navigated by ruling house. Each dynasty hub gathers its rulers, its coinage character, and its mints; the per-emperor pages carry the biographies.

The Julio-Claudians (Augustus to Nero) set the template — imperial portrait obverse, dynastic and political reverse. The Flavians gave us the IVDAEA CAPTA series and the Colosseum sestertius of Titus. The Nerva–Antonine period — Trajan, Hadrian, Marcus Aurelius — is the artistic peak of Roman portraiture; Hadrian's province and travel coinage is a self-contained collecting field. The Severans introduced the antoninianus and left an unusually rich coinage of imperial women. The soldier-emperors of the third-century crisis are the cheapest way into imperial silver. The Tetrarchy under Diocletian standardised the follis and the mint-mark system; the Constantinian house (Constantine I onward) brought the solidus and the first Christian coin types. The Valentinianic and Theodosian houses carry the Western series to its end in 476; the Eastern half simply continued.

For depth on the four rulers with full collector guides, start with Augustus, Trajan, Vespasian, and Constantine I. Republican and provincial money sit alongside the imperial series — see Roman Republican and Roman Provincial coinage.

Collecting and the market

The price ladder here is the longest in ancient numismatics: the same field that hands a beginner a Constantinian bronze for the cost of lunch will, at its top step, sell a fine-style early aureus for the price of a car. Reading from the bottom up: late Roman bronze of common emperors runs $15 to $60; mid-grade Severan denarii $80 to $200; a choice portrait sestertius of the Antonines $400 to $1,500; Julio-Claudian or other early gold aurei from a few thousand into the tens of thousands for fine style. Condition and strike drive those numbers far more than rarity for most types — a sharp common sestertius beats a worn scarce one at the table.

For verified attributions, the indispensable open reference is OCRE (Online Coins of the Roman Empire), the American Numismatic Society's RIC database built with partner museums; the British Museum and the Tübingen IKMK provide deep image archives. On the economic history, Kenneth Harl's Coinage in the Roman Economy (1996) and C. H. V. Sutherland's Roman History and Coinage (1987) are the standard accounts. NumisLens catalogues roughly 13,700 RIC types with reference images — browse the catalogue by ruler, mint, or denomination, or use it to attribute a coin you already own.

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