Augustus (27 bc–ad 14) based the coinage on the aureus of 1 42 of a pound of gold, equivalent to 25 denarii, each of 1 84 of a pound of silver, the metals being struck almost pure. The denarius was valued at 16 asses. Token coinage consisted henceforth of brass sesterces and dupondii (equal to four and two asses, respectively), with copper asses, halves, and quarters, the as being the most common. Nero in ad 64 lightened aureus and denarius to 1 45 and 1 96, respectively, but debasement of silver subsequently took place. Under Septimius Severus it reached 40 percent, and Caracalla issued a debased double denarius of the weight of only 1 1 2 denarii. Gallienus’ double denarius of copper and silver, leached to give a more silver-rich surface, marked a monetary breakdown, only partially cured when Diocletian and Constantine again made gold the firm basis for supplementary pure silver and abundant copper coinage.

Augustus’ earliest gold and silver were coined chiefly in the east—e.g., at Ephesus and Pergamum—and more briefly at Emerita in Spain. Bronze also was mainly eastern, though some was struck at Nemausus (Nîmes). The Rome mint was reopened about 20 bc for gold and silver and remained open for this purpose until about 12 bc; its bronze continued irregularly. From 12 bc, Lugdunum (Lyon), with other mints of uncertain identity, undertook the main western coinages in gold, silver, and bronze. After 64 Rome was once more the chief mint for all metals. Official mintages were supplemented by a mass of regional or local coinages, while official coinages from eastern mints provided necessary currency for local Roman frontier forces.

The bronze of Rome was marked S(enatus) C(onsulto) and continued to bear the names of the tresviri monetales—masters of the mint, now reduced to their traditional number—until 4 bc. But S C also appeared on bronze from Lyon and Antioch in imperial provinces, showing that whatever nominal senatorial rights of coinage still lingered on—the tresviri are known until the 3rd century—the emperor wielded effective control over all metals everywhere. This was logical, since his economic powers were equally comprehensive. In fact, the old senatorial mint was transferred from the temple of Juno Moneta on Rome’s Capitoline Hill and merged, probably after the fire of 64, with an imperial mint for gold and silver elsewhere in the capital. Henceforth, it worked in sections—six were normal later—controlled immediately by an imperial procurator and staffed by slaves or freedmen.

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Portrait of Nero on a bronze sestertius struck at the mint in Lyon, France, c. ad 64–66; in the British Museum. Diameter 36 mm.

Reproduced with permission of the trustees of the British Museum; photograph, Ray Gardner for The Hamlyn Publishing Group Limited

The use of Caesar’s own portrait upon coinage set a precedent; although under Augustus and Tiberius token denominations occasionally lacked the imperial portrait, it was thereafter an essential element of virtually every gold, silver, and bronze coin of the official mints, as also of nearly all provincial and local coins. Emphasis on the personality of the emperor (extended sometimes to empresses, sons, or deceased members of the imperial house) was a powerful propaganda instrument in a coinage that circulated throughout a vast empire. The great series of imperial portraits, from Augustus to Romulus in ad 476, is artistically outstanding. Many of the finest appeared on the large brass sesterces down to the 3rd century and on the even larger bronze medallions produced for presentation; but particular care was taken over the portraits for gold, which, being softer, showed a beautiful and highly sensitive impression. Nothing is known of the portrait artists, though it is likely that they were often from the Greek East.

Imperial reverse types, if artistically less remarkable, are uniquely important for the unparalleled fullness of the historical commentary that they supply. The major mints provided annual evidence of imperial interests: victories in war; frontier defense (e.g., Rex Parthis datus—“A king is given to the Parthians”—of Trajan); a well-earned peace (e.g., the Pace terra marique parta Ianum clusit—“There being peace on land and sea, the doors of the Temple of Janus were closed”—of Nero); the birth of an heir or alternative provision for the succession; public shows; acts of social reform or public relief (e.g., Civitatibus Asiae restitutis—“For the restitution of the citizenries of Asia”); imperial journeys (e.g., Adventus Augusti—“The arrival of the emperor”); and religious or other anniversaries (e.g., the Felix temporum reparatio—“Happy days are here again”—on Rome’s 1,100th birthday). Their interpretation demands care, since, being selected by imperial officials, their tenor can conflict with the attitude of anti-imperial historians. But they show the efforts made by emperors, as the omnipotent semireligious heads of a huge and heterogeneous empire, to conciliate and inform. They contributed powerfully to the growing conception of an eternal Roman empire, seen no less in the special types of eagle (the soul flown heavenward) or funeral pyre or temple in honour of “good” emperors consecrated as divi than in the annual record of military victory, economic security, and provincial peace and implicit in the regularity of imperial succession. The normal colour given to this imperial program was religious, for the coinage types commonly embraced such characteristically Roman concepts as Aequitas (Justice), Fides (Faith), and Concordia (Harmony)—social virtues operating in the guise of minor deities.

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Detail of a bust of Diocletian in the Capitoline Museum, Rome.

Alinari/Art Resource, New York

Diocletian’s institution of the tetrarchy, by which the empire was divided administratively between two Augusti and two Caesars, brought fundamental changes in social and economic policy; the instability of prices called for complete renewal of the monetary system. His coinage reforms took place in stages from about 286 to about 296. First, new aurei were struck at 60 to the pound of gold. Then, about 293–294, new silver coins, of good purity, were struck at the revised Neronian weight of 96 to the pound of silver. Finally, about 294–296, new copper coins appeared that were larger and intrinsically more valuable than the small debased double denarii of previous reigns. The contemporary names of these silver and copper pieces are not known. This reformed coinage was struck at a variety of mints from Londinium (London) to Alexandria, most of which coined in all three metals. Types were closely controlled in the silver and copper coinage; in the latter the almost universal type was for some years that of the “Genius Populi Romani.” The obverse bore the portrait of one or other of the tetrarchs, each of whom coined with portraits of all four.

The breakdown of the tetrarchy after 306 weakened the new system. Copper was quickly and steadily lightened, and silver struck very sparingly. Gold, however, continued in good supply; and though Constantine’s solidus showed a reduced weight standard, there was no shortage of gold throughout the rest of the 4th century. In time, silver coinage increased, especially after about 350, when the miliarense (1/1,000 of a gold pound) and smaller denominations appeared. By the end of the 4th century, however, the size of copper coins had dropped very sharply, and in the 5th, until the Western Empire collapsed in ad 476, the western coinage consisted finally of gold with a little silver, struck mainly from the mints of Ravenna and Rome.

From 312, when Constantine became emperor of the West, coin types began to show new tendencies. The imperial portrait was still the dominant feature. Reverses displayed complementary themes—the glory of the army, vows for continued imperial rule, the constant struggle against barbarian pressure on the frontiers. The old variety of pagan gods—Jupiter excepted—mainly disappeared, though Sol, popular from Aurelian onward, was used, especially by Constantine. Christian emblems did little to take their place, though the Christian monogram, the Greek letters chi and rho superimposed, sometimes on a standard, began to appear with Constantine and was combined with the alpha and omega under Constantius II and Magnentius. On the whole, however, there was an unavowed truce between Christianity and paganism, only occasionally broken, as when Julian revived a range of pagan types; the full development of the Christian tradition in coinage was reserved for Byzantium.