Coins of Diocletian, Roman emperor 284-305 and founder of the First Tetrarchy 

Diocletian became the Roman emperor ("Augustus") in the east in 284 CE and ruled until his abdication in 305. He promoted Maximian to co-Augustus in 286. In 293 he added two Caesars, Constantius and Galerius, making four simultaneous rulers, that is, a "tetrarchy." For a page devoted to the coinage of the First Tetrarchy, see here. For a short history of Diocletian see below on this page

Coin to the right: A large (28 mm) follis of Diocletian. IMP[erator] DIOCLETIANVS AVG[ustus]. His laureate and cuirassed bust right. Details of the coin are below. His full name was Gaius Aurelius Valerius Diocletianus. His coins usually just name him DIOCLETIANVS, but sometimes include "C C VAL" for Caesar Gaius Valerius. 

Events that significantly changed the coins of Diocletian are listed next and linked to coins illustrated below on this page.

1)  284.  Diocletian became Augustus and began issuing radiate coins (called aureliani or antoniniani) much like those of previous emperors. (This page does not discuss his gold coins.)
2)  286.  Diocletian promoted Maximian to co-emperor in the west. Reverse legends that ended "AVG" changed to end "AVGG." 
3)  293.  Promoted Constantius and Galerius to Caesars in the west and east, respectively. Coins in their names were added, but coins in the name of Diocletian did not change.
4)  c. 294.  Began a coin reform that changed the denominational system, adding in the follis (a.k.a. nummus), silver argenteus, and (in the east) the "radiate fraction" (a.k.a. Post-reform radiate) that had the appearance of, but less silver than, the previous radiates.  Production of the previous radiates was discontined
5)  296-7.  Maximian went to North Africa to quell a rebellion and opened the Carthage mint which minted reverse types unique to Carthage
6)  298.  Trier (only Trier) minted FORTVNA REDVCI types for the safe return of emperors from their travels. 
7)  300.  In 300 concerns about inflation prompted a new type--the SACRA MONETA type--which was introduced to emphasize the sacred nature of coinage and its value. In 301 Diocletian issued a Currency Edict and the "Edict on Maximum Prices" to dictate prices. Apparently the nominal values of some of the existing denominations were changed, but little is visible in the coinage other than the new SACRA MONETA type. 
8)  305.  Diocletian and Maximian retired May 1, 305. Retirement/abdication types began.
9)  c. 308.  Retirement issues for Diocletian were discontinued.
This page ends with some other types.  References are at the end


Event 1)  Diocletian issued aureliani which were often marked XXI to denoted 20 parts copper and 1 part silver. They come with very many different reverse legends and designs. A page devoted to aureliani of Diocletian is here.

23-22 mm. 3.93 grams.
RIC 161 "Rome, 285."
Sear 12665.
Coins with reverse legends terminating with one "G" like this one are from Diocletian's sole reign before Maximian was elevated to co-Augustus.

Diocletian had Jupiter (IOVE) as his patron god and this type proclaims that "Jupiter protects the Augustus"


Event 2)  After Maximian was promoted to co-emperor, the reverses of aureliani that had ended "AVG" for Augustus had new legends ending "AVGG" where the 2 G's indicate two emperors. 

23 mm. 4.32 grams.

CONSERVATOR AVGG  [The two G's make it after Maximian was elevated to co-Augustus]
Emperor on left and Hercules on right holding pateras over altar in the middle. The emperor holds a long scepter in his left hand and Hercules rests his left hand on a club.
Coded mintmark •XXI•BI•,  Γ in field left
RIC 264F.
Sear 12640 BI.
Aureliani of Diocletian are common, although among the many types some are rare and expensive. 
     (For many more aureliani of Diocletian, see here.  For more about the so-called "coded" series, see here.)  
Event 3)  Coinage began to be issued for Constantius and Galerius as Caesars (see here for their aureliani), but this event is not visible on the coinage in the name of Diocletian. 

Event 4A)  The large (c. 28 mm and 10 grams) "follis" was introduced and had legend "GENIO POPVLI ROMANI" (Spirit of the people of Rome). There were about a dozen mints and each had a different mintmark in exergue (below the line on which Genius stands), so it is easy to tell where they were minted.  

[The obverse is the top image on this page]
27-26 mm. 9.23 grams.
GENIO POPVLI ROMANI, Genius standing left holding patera and cornucopia.
S in left field, F in right field
IITR in exergue, for the second officina of TR[everi] = Trier.
RIC Trier 524a "c. 302-303."
Sear 12762. Failmezger 6.

Folles of Diocletian are very common and often come in nice condition and this is the most common type. 


    (For a page on GENIO POPVLI ROMANI folles from various mints, see here.)

4B)  The new good-silver argenteus was introduced. Silver coins of that quality had not been issued since Nero (54-68), over two hundred years earlier. There are several reverse legends and types.

20-19 mm. 3.30 grams.
"XCVI" is "96" in Roman numerals and gives its value, "96 to the Roman pound of silver." The portrait is in high relief which is common on argentei but not seen on the previous aureliani nor the accompanying folles and radiates. 
T below for Ticinum.  
RIC VI Ticinum 20a, "c. 300."
Sear 12620.

Argentei of Diocletian are rare and expensive.

   (For more about argentei, see here.)

Event 4C) The radiate fraction was introduced at eastern mints. It looks very much like an aurelianus, but has no added silver and is, consequently, of much lower intrinsic value. Almost all of them have the legend CONCORDIA MILITVM except for those issued at Carthage with vota types.

21 mm. 2.78 grams. 
Radiate fraction, a.k.a. post-reform radiate.

  HB in field for Heraclea, officina B.

RIC Heraclea 13.
Sear 12833. Failmezger 11.

Radiate fractions of Diocletian are common.

 (For much more about radiate fractions, see here.)

Event 5) Maximian went to north Africa to quell a rebellion and opened the Carthage mint which minted the new denominations with reverse types unique to Carthage.  

29-27 mm. 9.48 grams.
Africa standing facing with elephant-skin headdress, holding standard and elephant tusk, tiny lion on bull at feet.
 I  in field  (for Jove, the coins for Maximian have H for Hercules)
PKP  in exergue  (K is for Carthage)
RIC Carthage 23a "297-8."
Sear 12754. Failmezger 1.

Celebrates the happy arrival of Maximian at Carthage (with Diocletian included in the issue as Maximian's colleague).



28-25 mm. 7.77 grams.

Carthage standing holding fruits in both hands
  A in exergue
RIC Carthage 31a "c. 299-303."
Sear 12828. Failmezger 9.
Radiate fractions with vota types were issued at Carthage, Rome, and Ticinum.

21 mm. 2.86 grams.
A "radiate fraction".


 FK    (Felix Karthage)
in wreath
RIC Carthage 37a "c. 303" [but, I think it is from earlier, from c. 296-7].
Sear 12843. Failmezger 40.

Carthage also had its own argenteus types, not illustrated here. 
Event 6)  Trier (and only Trier) minted FORTVNA REDVCI types for the safe returns of emperors from their travels. 
Fortuna seated left, holding rudder on globe and cornucopia
RIC Trier 230a "c. 298-9."
Sear 12755. Failmezger 4.
According to RIC, the first issue (distinguished by this mintmark TR, as opposed to BTR or ATR) refers to
"Constantius' successful Rhenish campaigns" and possibly the conclusion of his British campaign in 296-297, and
"Heraclius' [Maximian's] African campaign (followed by his visit to Rome)" which followed his return from the Rhine (on his way to Africa).

   (For much more about FORTVNA types, see here.)
Event 7)  In late 301 Diocletian issued a Currency Edict and the "Edict on Maximum Prices" to deal with inflation. Apparently the nominal values of some denominations were changed, but little is visible in the coinage other than that c. 300 the SACRA MONETA type was introduced to emphasize the sacred nature of coinage. 

27 mm. 10.04 grams.
Moneta holding a balance and cornucopia.
AQP  in exergue for Aquileia, officina Prima

RIC Aquileia 35a "c. 302-303."
Sear IV 12820. Failmezger 28.

This reverse design is the second-most common type of follis. It appears from five mints with numerous legend variants. 

     (For more about the SACRA MONETA type, see here.)

Alexandria minted a new type c. 304-5.

27 mm. 9.46 grams.
S   P
ALE in exergue for Alexandria.
RIC Alexandria 41 "c. 304-5."
Sear 12805. Failmezger 27.
Alexandria is the only mint for this type, which was also minted for Galerius (the other Jovian emperor). A corresponding type, HERCVLI VICTORI, was minted in the same issue at Alexandria for the Herculian emperors Maximian and Constantius.
This type is scarce.

Event 8) Diocletian and Maximian retired May, 1, 305, after which retirement issues were issued for both,

27 mm. 8.28 grams.
Laureate bust right in imperial mantle, holding olive branch (symbolizing peace) and mappa (a cloth dropped by the emperor to start chariot races).
"SEN AVG" for "Senior Augustus" is a new title for the retired emperors.

Providential and Quies standing facing each other,
S  F in fields (Saeculi Felicitas?)
KS low in middle field, likely for Cyzicus.
PTR in exergue
RIC Trier 677 "1 May 305 - early 307."
RIC attributes this coin to Trier because of the "PTR" mintmark, but Bates argues that this coin was really minted at Cyzicus. 
Sear 12928. 
Failmezger 52 .

    (For much more about retirement issues, see here.)
Event 9)  Abdication/retirement types were discontinued for Maximian when he resumed the title Augustus c. late 306 under his son Maxentius. Diocletian's retirement types continued a while longer, perhaps into 308. 

Other types.  It seems that almost every emperor minted a few unusual types that played almost no role in the monetary system. We wonder why they bothered and what the coins were good for. Here are two rare coins of unusual denominations.

22 mm. 4.12 grams.

RIC V.II 202, Rome, 285. "R3."
Sear 12830.

This laureate denomination is sometimes called an "as". 
Why it was minted is not known.

14 mm. 2.00 grams.
"Fraction"  Maybe 1/8 follis? 
in wreath
RIC Trier 610a "R4" "c. Sept. 303."

Zschuke 4.2. Sear 12847. Failmezger 38.
This denomination seems to begin at Trier c. 290, before the coin reform of c. 294. They are rare today and likely to have been rare then. What were they good for?  Gifts at games?
  (For much more about fractions, see here.)

Finally, Diocletian minted Roman Egyptian tetradrachms at Alexandria.

19 mm. 7.56 grams. Thick.
Tetradrachm of Roman Egypt minted at Alexandria
L H (for year 8)
Jupiter seated left holding out patera and holding vertical staff.
Sear 12882. Emmett 4089. 

Other Roman provincial mints had discontinued production long before, but Alexandria continued minting tetradrachms until year 12 of Diocletian (296).

Emmett lists over 100 varieties of tetradrachms of Diocletian. They are common and inexpensive. 

History of Diocletian

Diocletian becomes emperor. In 284 Carus was the senior Augustus and his two sons Carinus and Numerian were co-Augusti. Carus went east accompanied by Numerian, with Diocletian one of his generals, with plans to regain Mesopotamia from the Sasanians. Carinus stayed behind to take care of the rest of the empire. Carus successfully captured the Sasanian capital, Ctesiphon, but was later found dead in his tent after a thunderstorm. The romantic story is he was struck by lightning, however subsequent events suggest he was murdered by the praetorian prefect Arrius Aper. Numerian inherited the war and made peace on favorable terms. However, while returning from Mesopotamia he, too, was found dead. This time Aper was accused of murder and was executed. On the spot Diocletian was chosen emperor by the army. That left Carinus still Augustus in the west. After dealing with the usurper Julian of Pannonia, Carinus went east to confront Diocletian. The story is that Carinus was a womanizer and while Diocletian appeared to be losing a decisive battle with Carinus, Carinus was assassinated by an officer whose wife he had seduced.  Diocletian inherited the empire. 

Diocletian as Emperor.  He is perhaps best known for voluntarily retiring (admittedly, after being quite ill) after a long reign of over twenty years. Much of Diocletian's impact was not because of glamorous wars, rather because of his dramatic changes of the day-to-day administration of the empire. Of course, he is famous for introducing the tetrarchy of four simultaneous rulers, but that is only the most visible (especially on coins!) of his many administrative changes that subdivided responsibilities. Diocletian dramatically increased the number of provinces by dividing old provinces into smaller regions and he separated their civil and military positions. This made it more difficult for any governor or general to command the resources to revolt. He reformed taxes by introducing an annual budget with fixed annual tax requirements on all parcels of land, according to their productivity, to be paid in kind, and on livestock and on people (a woman counted as half a man). Taxes had not been reformed for centuries, much valuable land had been untaxed, and taxes had been collected erratically with many rich people being able to evade them. His tax Edit of 297 was intended to raise more money for the state, but in a fair manner.  Also, it hoped to reduce inflation by pegging taxes to goods instead of to gold and silver coins. (Later the system was abused by raising the tax requirements to impossible levels.) He required sons to take up the professions of their fathers--a very strict way to make sure that arable land retained farmers, armies had soldiers, and guilds had members. For example, if a man married the daughter of a miller, he was required to become a miller. Freedom was curtailed.

Modern markets rely on price incentives to shift supplies and people around to necessary and productive uses, but Diocletian and subsequent rulers saw that markets did not get the necessary jobs done, so they decreed they be filled by people who knew how to do them--the sons of people who had done them. 

As usual, there were some wars with foreign adversaries. Conflicts with the Sasanians provoked a line of defensive forts on the eastern frontier; the remains of some are still visible in the eastern deserts.Diocletian's recognition that the empire was too large for one person to rule and the west and east each needed their own emperor turned out to be correct, even though Constantine was later able to unify the empire for a few years before it was again divided among his children. 

When Diocletian retired in 305 and forced Maximian to retire with him, the Caesars became the new Augusti and two new Caesars were appointed, giving hope that the tetrarchic system would continue. However, when Constantius, a new Augustus of the Second Tetrarchy in the west, died in July 25, 306, the system of orderly succession of four rulers fell apart. Nevertheless, many of Diocletian's other administrative changes remained. Later rulers doubled down on Diocletian's methods of filling jobs and financing the government. His impact was long lasting. 


References. (In order of usefulness, not alphabetical order.)

RIC VI, Roman Imperial Coinage, volume VI, by C. H. V. Sutherland, 1973. This volume covers the post-coin-reform period. Many varieties have been discovered since this book was published, but there is no easy way know more than is in this book. Many collectors use RIC solely to provide identification numbers, but it has far more interesting information than just that, including lots of history and chronology with relevant coin evidence.

RIC V, part II. Roman Imperial Coinage, volume V, part II, by Percy H. Webb, 1933.  This volume covers the antoniniani of the tetrarchs, but is very old and many variants have been discovered since then. 

Failmezger, Victor. Roman Bronze Coins from Paganism to Christianity, 294-364 A.D. 2002. A complete list of types (but not mints, varieties, and RIC numbers) from the coin reform to 364, with very many color photos and short outlines of the history, with chapters on collectible types like the "fallen horseman" coins of the coin reform of 348. I love this book and use it to keep track of types.

Sear, David. Roman Coins and their Values, volume 4. 

Zschucke, Carl-Friedrich. Die Bronze-Teilstück-Prägungen der römischen Münzstätte Trier. 1989. Small paperback. 65 pages with over 200 fractions illustrated.

Emmett, Keith. Alexandrian Coins. 2001. Large hardcover with a complete list of Alexandrian types. A few photos throughout and 13 plates of fine line drawings.  

Williams, Stephen. Diocletian and the Roman Recovery. 1985.   Not a coin book, rather a biography of Diocletian which includes a substantial look at how his reforms played out through the time of Constantine.   [p. 119ff discuss how he changed taxes and employment.] 


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