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The Great Reformer: The Coins of Diocletian

By Mike Markowitz for CoinWeek …..

THE ABUNDANT AND complex coins of Diocletian document a period of profound change in Roman history.

In November 284, Roman soldiers escorting the ailing emperor Numerian’s coach across Anatolia smelled a foul odor. When they opened its curtains, they found the emperor had been dead for some time. Suspicion fell on Lucius Flavius Aper, the Praetorian Prefect[1]. Diocles, commanding the imperial bodyguard, accused Aper of murdering the emperor and executed him on the spot. The legions immediately proclaimed Diocles as emperor, who renamed himself Diocletianus–usually written in English as “Diocletian”.

A tough soldier of humble origin from Dalmatia (the coastal region of modern Croatia), Diocletian would rule for 20 years, ending the chaotic “military anarchy” that had tormented the empire for five decades. Realizing that the Roman Empire had become too large for one man to manage, he made his trusted friend Maximianus co-emperor in the West, ruling from Trier in Germany and later from Milan in Italy. Diocletian himself ruled in the East, establishing his capital at Nicomedia (modern Izmit, Türkiye). To ensure a smooth succession, each emperor later appointed a junior colleague (designated as Caesar) in a system that historians call the Tetrarchy[2]. Maximian chose Constantius Chlorus as his junior colleague, while Diocletian chose Galerius, sealing the deal by giving Galerius his daughter in marriage.


Diocletian Gold Aureus. Cyzicus Mint. 284-286. Image: CNG.
Diocletian Gold Aureus. Cyzicus Mint. 284-286. Image: CNG.

Roman soldiers during this era expected to be paid in gold. Although the purity of the metal was maintained, the weight of the gold aureus declined sharply during the second half of the third century CE, becoming so inconsistent that the coins traded by weight. Early in his reign, Diocletian issued aurei of 6.5 grams at a standard of 50 to the 12-ounce Roman pound. This was later reduced to a standard of 60 to the pound (5.3 grams). One source (Sear, 79-89) lists 97 different aurei coins in the name of Diocletian alone, and additional joint issues that depict him and his co-emperor Maximian.

The emperor’s stern portrait features a laurel wreath, a short beard, and a military haircut. The reverse typically bears the standing figure of Diocletian’s patron deity Jupiter with an eagle and the inscription IOVI CONSERVATORI AVG (“To Jove, Preserver of the Emperor”)[3]. An example graded “Choice AU, High relief and perfectly centered” brought $16,000 in a 2023 U.S. auction.


Gold Quinarius. Image 290-294. Image: Numismatica Ars Classica.
Gold Quinarius. Image 290-294. Image: Numismatica Ars Classica.

The gold quinarius, valued at half an aureus, was issued in very small quantities. About eight different types of Diocletian are known. Having a smaller blank (about 16 mm) to work with, the engraver abbreviated the emperor’s title and dispensed with the little eagle at Jupiter’s feet[4].

Gold Medallion

Gold Medallion of Ten Aurei. Aquileia Mint. 294. Image: CNG.
Gold Medallion of Ten Aurei. Aquileia Mint. 294. Image: CNG.

While not quite a coin, a gold medallion (denio) of 10 aurei (53.65 grams) was struck for Diocletian in 294 at the mint of Aquileia in northern Italy, possibly for the 10th anniversary of his reign. The emperor is bare-headed, his thick, muscular neck conveying a message of strength. The reverse depicts Jupiter enthroned, holding a thunderbolt, with an eagle at his feet. These massive and very rare medallions were probably intended as diplomatic gifts or presentation pieces for high officials.

A cataloguer wrote:

The task of creating dies for such an impressive medallion was bestowed on an experienced engraver of singular talent. The portrait, while reflecting some of the stylized Tetrarchic artistic conventions of the time, is still highly individualistic and conveys Diocletian’s dominating personality… His military origins are revealed in the close-cropped haircut and trim beard. Remarkably, the head of Diocletian is shown plain and unadorned without a laurel wreath, cuirass, cloak, or other symbol of rank[5].

This was the largest Roman gold medallion offered at auction in over a hundred years, and brought $2.3 million including the buyer’s fee!


Bronze Antoninianus. Cyzicus Mint. 290-292. Image: CNG.
Bronze Antoninianus. Cyzicus Mint. 290-292. Image: CNG.

The antoninianus was introduced by Emperor Caracalla in 215 CE at a value of two denarii, even though it contained silver worth only 1.5 denarii. During the third century, the percentage of silver in the antoninianus was gradually reduced, falling below 5% as emperors were forced to stretch a limited supply of bullion to pay their troops. Widespread counterfeiting made the situation worse.

The usual mark of denomination for the antoninianus was the spiked “radiate” crown worn by the emperor on the obverse. A coin from the mint of Cyzicus under Diocletian bears the reverse inscription CONCORDIA MILITVM (“Harmony of the Soldiers”). The image shows a standing figure of Jupiter handing a statuette of Victory on a globe to the emperor. A bold Roman numeral XXI appears below[6]. This has been interpreted either to indicate that the coin contained one part silver to 20 parts bronze or that the alloy contained 20 obols of silver (14.4 grams) for each libra (327 grams) of bronze (about 4.4%). Well-preserved examples have a surface that is nearly completely silvered. There are various theories about how this enriched surface coating was created.

Silver bronze Antoninianus. Image: Leu Numismatik AG.
Silver bronze Antoninianus. c. 293. Image: Leu Numismatik AG.

On an example dated to 293 from the mint of Lugdunum (today Lyons, France)[7], the radiate crown is combined with a crested military helmet. The reverse bears a standing figure of the war goddess Minerva with the ironic inscription PAX AVGG (“Peace of the Emperors”). The two Gs in the inscription indicate that Augustus is plural.


Silver Argenteus. Siscia Mint. 294-295. Image: CNG.
Silver Argenteus. Siscia Mint. 294-295. Image: CNG.

As part of a major coinage reform in 294, Diocletian introduced a new coin called the argenteus, a high-value piece of nearly pure silver (95% or better). One gold aureus was worth 25 of these argentei. A common reverse[8] depicted the four rulers of the Tetrarchy standing before the gate of a walled city, with the inscription VIRTVS MILITVM (“Valor of the Soldiers”). These coins were introduced at a value of 25 denarii communes (abbreviated d.c.),  an accounting unit that would eventually be introduced as a small copper coin, the “post-reform laureate”. The value soon rose to 50, and later 100, denarii communes.

Argentei were often hoarded as soon as they were issued, and many are found in near-mint condition.

Silver Argenteus. Image: CNG.
Silver Argenteus. Image: CNG.

On some later argentei, the reverse bears the number XCVI, indicating that 96 coins were struck from each Roman pound of silver, for a theoretical weight of 3.40 grams. An example from the mint of Aquileia, graded “near EF” actually weighs 3.63 grams[9].


Bronze Follis Aquileia Mint. Image: CNG.
Bronze Follis Aquileia Mint. Image: CNG.

Another coin introduced as part of Diocletian’s currency reform in 294 was a large silvered bronze piece of about 10.3 grams called a “follis” or billon “nummus” by modern numismatists; its ancient name is uncertain. The weight of the follis, and the percentage of silver in the alloy, declined steadily over the next 20 years. An example dated to circa 300 CE from Aquileia bears the inscription SACRA MONETA AVGG ET CAESS NOSTR (“Sacred Mint of Our Emperors and Caesars”) surrounding the figure of Aequitas, the personification of fair trade, holding her scales[10].

Bronze Follis, Abdication issue. Serdica Mint. Image: CNG.
Bronze Follis, Abdication issue. Serdica Mint. Image: CNG.

On May 1, 305, at the age of about 60, Diocletian announced his abdication. He retired to his vast fortified palace[11]–which still stands–at Split on the Adriatic coast, where he was particularly proud of the cabbages he grew in his garden. An extensive issue of coinage celebrated this unprecedented event[12]. The coin’s obverse inscription is DN DIOCLETIANO FELICISSIMO SEN AVG (“To Our Lord Diocletian, Most Fortunate Senior Augustus”). The emperor wears the elaborately embroidered “consular” toga and holds an olive branch. On the reverse, we see the standing female figures of Providentia, the personification of forethought, and Quies, the personification of tranquillity – a suitable image to mark retirement.

The date of Diocletian’s death is uncertain; some sources place it as early as 311, others as late as 316.

Reduced Sestertius

Bronze Reduced Sestertius. Image: Nomos AG.
Bronze Reduced Sestertius. Image: Nomos AG.

The large bronze or brass sestertius was an important denomination for the everyday Roman. Even very large sums of money were often expressed in terms of sestertii. Originally valued at one-quarter of a denarius, the weight and value of the coin steadily declined during Imperial times. Before his great coin reform of 294, Diocletian issued a small quantity of “reduced sestertii” (about 5.5 grams), which are quite rare today[13]. The reverse bears a standing figure of Jupiter, the emperor’s patron god.

Post-Reform Radiate

Bronze Post-Reform Radiate. Image: Agora Auctions.
Bronze Post-Reform Radiate. Image: Agora Auctions.

The bronze “post-reform radiate” of about four grams bears the usual CONCORDIA MILITVM inscription[14]. The rather awkward name is modern; as usual, we don’t know the coin’s ancient designation. Originally valued at 2 d.c., the coin was revalued to 5 d.c. in 301 and soon disappeared from circulation.


Silvered bronze Denarius (21 mm, 2.80 g,), Rome, 286. Very rare.  Image: Leu Numismatik AG.
Silvered bronze Denarius (21 mm, 2.80 g,), Rome, 286. Very rare. Image: Leu Numismatik AG.

Diocletian was the last emperor to issue a denarius[15], which by this point had been reduced to a silvered bronze piece of just 2.8 grams or less (for comparison, the U.S. cent weighs 2.5 grams). The emperor wears a laurel wreath rather than the radiate crown. Surviving examples are extremely rare, and the coin may have served some ceremonial purpose, such as being thrown to the crowd at Imperial celebrations.

Post-Reform Laureate

“Post-reform laureate,” (d.c.) after 294. Bronze, Ticinum mint (16mm., 1,17g.) VTILITAS PVBLICA. Image: Savoca Numismatik GmbH & Co. KG.
“Post-reform laureate,” (d.c.) after 294. Bronze, Ticinum mint (16mm., 1,17g.) VTILITAS PVBLICA. Image: Savoca Numismatik GmbH & Co. KG.

The smallest denomination after the coinage reform of 294 is the“post-reform laureate”, also called a bronze quinarius, a quarter-follis, or simply a “fraction” by cataloguers. Weighing a bit over a gram, this coin was probably worth just one denarius communis. The emperor wears a laurel wreath. The reverse bears the odd inscription VTILITAS PVBLICA (“Public Utility”) with the standing figure of Utilitas, the personification of usefulness[16]. These low-value coppers are quite scarce, and most specimens probably went into the melting pot over the following decades.

Collecting the Coins of Diocletian

Standard references for the coinage of Diocletian, usually cited in sale catalogs, are Volume V, Part 2, and Volume VI of Roman Imperial Coinage (often abbreviated as RIC). Secondhand copies are scarce and typically sell for around $150 each. A more accessible reference for most collectors is the American Numismatic Society’s (ANS) Online Coins of the Roman Empire (OCRE).

In 1889, the British numismatist Seth Stevenson wrote this assessment of Diocletian:

As emperor, Diocletian exhibited in his administrative capacity the skill and courage of a great commander, combined with abilities of the highest order for civil government… But his plans, however well concerted and energetically carried into effect, being founded on the necessity of pressing emergencies, scarcely remained in effective operation during his own lifetime, and at his death fell to pieces amidst the sanguinary struggles of rival Emperors and Caesars (Stevenson, 330).

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[1] https://en.wikipedia.org/wiki/Praetorian_prefect

[2] https://en.wikipedia.org/wiki/Tetrarchy

[3] CNG Auction 123, May 23, 2023, Lot 678. Realized $16,000 USD (estimate $10,000).

[4] NAC Auction 41, November 20, 2007, Lot 138. Realized CHF 10,000 (about $9,006 USD; estimate CHF 7,500).

[5] CNG Triton XXVI, January 10, 2023, Lot 830. Realized $1,900,000 USD (estimate $500,000).

[6] CNG Triton XXVII, January 17, 2024, Lot 6320. Realized $375 USD (estimate $100).

[7] Leu Web Auction 29, February 24, 2024, Lot 2340. Realized CHF 65 (about $74 USD; estimate CHF 25).

[8] CNG Triton XXVII, January 9, 2024, Lot 866. Realized $1,500 USD (estimate $750).

[9] CNG Triton XXVII Online, January 17, 2024, Lot 6317. Realized $800 USD (estimate $300).

[10] CNG E-auction 558, March 20, 2024, Lot 672. Realized $180 USD (estimate $100)

[11] https://en.wikipedia.org/wiki/Diocletian’s_Palace

[12] CNG E-auction 557, March 6, 2024, Lot 435. Realized $400 USD (estimate $150)

[13] Nomos obolos 2 sale, June 14, 2015. Realized CHF 240 (about $259 USD; estimate CHF 200).

[14] Agora auction 64, January 24, 2017, Lot 267. Realized $30 USD (estimate $50)

[15] Leu auction 7, October 24, 2020, Lot 1696. Realized CHF 1,200 (about $1,323 USD; estimate CHF 750).

[16] Savoca Auction 21, March 11, 2018, Lot 388. Realized €360 (about $443 USD).


Bowman, Alan K., et. al. The Cambridge Ancient History, Volume XII: The Crisis of Empire, AD 193-337. Cambridge (2008)

Cope, L.H. “The Argentiferous Bronze Alloys of the Large Tetrarchic Folles of AD 294-307”, Numismatic Chronicle (1968)

Failmezger, Victor. Roman Bronze Coins: From Paganism to Christianity, 294-364 AD. Washington (2002)

Harl, Kenneth W. Coinage in the Roman Economy: 300 BC to AD 700. Baltimore (1996)

Mattingly, H. Roman Imperial Coinage, Volume V, Part 2: Probus to Amandus. London (1968)

Meyer, James. “Silvered Bronzes of Diocletian”, The Celator 5 (July 1991)

Sear, David. Roman Coins and Their Values, Volume IV. London (2011)

Stevenson, Seth W. A Dictionary of Roman Coins. London (1964; reprint of 1889 edition)

Sutherland, C.V.H. Roman Imperial Coinage, Volume VI: Diocletian to Maximinus. London (1967)

Toynbee, J.M.C. Roman Medallions. New York (1985; reprint)

Vagi, David. Coinage and History of the Roman Empire (2 volumes). Sidney, OH (1999)

Zarrow, Edward. “Diocletian and Images of Imperial Concord”, The Celator 12 (September 1998)

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Mike Markowitz
Mike Markowitz
Mike Markowitz is a member of the Ancient Numismatic Society of Washington. He has been a serious collector of ancient coins since 1993. He is a wargame designer, historian, and defense analyst. He has degrees in History from the University of Rochester, New York, and Social Ecology from the University of California, Irvine. Born in New York City, he lives in Fairfax, Virginia.

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