The mainstay Roman coin through the Severan dynasty—the middle of third century AD—was the pure silver denarius. A smaller silver coin of half the weight was infrequently struck, called the quinarius. The main bronze coin was the sestertius (a denarius was worth 4 sestertii), with the gold coin being the aureus. By the end of the Severan years, the silver coins were getting increasingly debased, so that a new coin was introduced, worth 2 denarii, called the antoninianus. The antoninianus gradually replaced the denarius as the workhorse common coin. As all the coins became more and more debased—containing more and more bronze, and less and less silver—the traditional bronze denominations became increasingly useless.

By the time Diocletian assumed power, all of the existing mints were striking massive numbers of base antoniniani (bronze with a slight silver wash), while other denominations were struck rarely. Rome was one of the few mints that continued to strike traditional denarii & quiinarii, albeit in very small numbers. By this time the denarius had devolved to a completely base bronze fraction with no silver at all. This page has examples of the three formerly silver coins as struck by the Rome mint just before Diocletian's coinage reform in 294.

When Diocletian instituted his massive new coinage in 294, the common antoninianus was preserved as a fraction of the new silvered bronze nummus ; the other traditional denominations were swept away. The nummus was supposed to fill the role of the sestertius as the standard coin for common transactions, while the denarius was replaced by the argenteus.

204-257

(click image to see larger picture)

Diocletian augustus

—struck by Diocletian

Rome, 285

obv.- IMP DIOCLETIANVS AVG; Laureate draped cuirassed bust right

rev.- VICTORIA AVG; Victory walking left, holding wreath and palm

RIC V.ii Rom 188

18mm; 2.3g; denarius

Rare bronze denarius; this denomination was struck only at Rome, and infrequently at that. This coin is one of the very first coins from the whole Tetrarchy era; it was struck at the very beginning of Diocletian's reign, before Maximianus was appointed co-ruler. This coin represents, essentially, the last denarii struck in the empire. Rated R2 in RIC.

204-260

(click image to see larger picture)

Diocletian augustus

—struck by Maximianus

Rome, 290

obv.- IMP DIOCLETIANVS AVG; Radiate, draped, and cuirassed bust right

rev.- IOVI FVLGERATORI; Jupiter standing facing, head right, preparing to hurl thunderbolt; at feet to left, eagle standing left, head right; XXIΔ

RIC V.ii Rom 168

23mm; 4.04g; antoninianus

From the White Mountain collection.

204-089

(click image to see larger picture)

Maximianus augustus

—struck by Maximianus

Rome (?)

obv.- MAXIMIANVS AVG; laureate bust right

rev.- HERCVLI DEBALLAT; Hercules, stg.l., holding club and lion’s skin, fighting Hydra

RIC – ; King, Roman Quinarii p.424, no. 2

16mm; 1.13g; quinarius

Rare and uncataloged variety, it's not clear where and when this was struck. Note from dealer:

Cathy King notes on p.241 of her book that aurei with this reverse type were struck at the mints of Trier and Siscia, but she can’t decide where the quinarius might have been struck (courtesy to C. Clay for this paraphrasis). But when the choice is between these two mints – the type could be struck at yet another mint where no aurei of this type are known – then the Siscia mint is most probable, if style is taken into account. Extremely rare, third specimen known (the other two: Arethusa 4, Lugano (1996) lot 670, cited by King, and another in a private collection).

My own opinion is Rome mint, based on the pattern of other small issues of fractions and also the portrait style. RIC attributes an issue of small unmarked fractions to 305; alternatively, this could have been struck before the coinage reform, when other quinarii and denarii were struck at Rome in the years before 294.

Diocletian's reign—and later, Constantine's—captured a significant transition in the political status of Rome. Before Diocletian, the "Roman empire" was organized as a large number of provinces that were administered by the government of the city of Rome. Most of the territory in the Italian peninsula was considered to be, administratively, part of Rome. Hence its people were Roman citizens, and exempt from taxes. "Rome" the empire was funded largely by taxes remitted from the provinces.

By the middle of the third century, Rome's effective political importance was receding rapidly. Breakaway states were established in Gaul, Britain, and Syria; barbarian invaders moved through the Balkans, Asia Minor, and Italy itself; and new emperors came to power from the provinces via control of their legions, and rarely, if ever, visited Rome itself.

One of Diocletian's great reforms was reorganizing Roman territory into a new system of provinces and dioceses, in which Rome, and Italy, became just one of several provinces. This is kind of like the US abolishing the District of Columbia and making Washington just another city in Maryland. Citizens of Rome, and Italy, also lost their exemption from taxation and would be treated like any other citizens. Instead of residing in Rome, Diocletian established his capital at Nicomedia; his co-emperor, Maximianus, established the western capital at Mediolanum in northern Italy, a further blow to Rome's status.

Rome fell in the administrative sphere of Maximianus, along with the other Italian mints. Like them, all the bronze coins initially were of the Genius type, followed by the "Sacra Moneta" motif after 301. Moneta types persisted at Rome throughout the brief reign of Severus, who nominally succeeded Maximianus as ruler of Italy in 305, until the revolt of Maxentius. Rome never strikes the military types that characterized Ticinum and Aquileia during this period, perhaps reflecting a lack of effective direct control of the city.

Rome mint under Maxentius. The unpopularity of Diocletian's reforms in Italy created the conditions that enabled Maxentius to successfully rebel and take control of Rome and the rest of Italy in 306. Maxentius' coinage expresses the emotional appeal of his political program. Traditional civic symbols of Rome—the Temple of Roma, the Dioscuri, wolf-and-twins, and Victory—are featured on his coinage, completely replacing the empire-wide motifs such as Genius Populi Romani that were intended to convey imperial unity.

Maxentius struck numerous coins at Rome in the name of Constantine, his supposed ally against the eastern emperors—at least until his break with Constantine in 308. He also struck numerous coins in the name of his father, Maximianus, who was installed as his co-ruler. His initial claim to power rested on his descent from Maximianus and his alliance with Constantine. No coins were struck for Galerius, Licinius, or Maximinus—except, curiously, a commemorative coin on the death on Galerius.

Rome mint under Constantine. Constantine initiated another wholesale reform of the coinage when he took control of the city. "Genius" coins were struck again, emphasizing Rome's re-integration with the empire. Sol was introduced with the same design as Constantine's other mints. Constantine also struck coins commemorating his victory and control of the city: SPQR OPTIMO PRINCIPI—"The Senate and People of Rome, to the best of Princes." Under Constantine, the Rome mint also again struck coins in the names of the other imperial colleagues, Licinius and Maximinus II.

Constantine's conquest of the city in 312 was the linchpin of a crucial period in Christian, and Western, history. In 311, Galerius died and cancelled the last great Christian persecutions. In 312, Constantine defeated Maxentius under a Christian flag at the Milvian Bridge, leading directly to the Edict of Milan in 313 that legalized Christianity. Also in 313, the violently anti-Christian Maximinus II (who had succeeded Galerius in the East) committed suicide after his defeat by Licinius.

Constantine took additional, decisive steps that furthered Rome's political decline, culminating in the refounding of Byzantium as the new capital of Constantinople, including a new Senate to rival Rome's. However, at the same time, the Church at Rome benefitted greatly from his patronage. Constantine donated the Basilica of St. John Lateran to the Church and constructed the Lateran Palace, which were consecrated in 324 as the seat of the Pope. He also began constructing St. Peter's Basilica in 323. By greatly increasing the status of the Church and the Pope, while continuing to deemphasize Rome's political importance, Constantine emphatically began to transform Rome's role from political capital to a religious one, controlled by the Church and Pope.