The translation of the codewords AEQVITI, IOBI and HPKOYΛI

by Gert Boersema

Like many collectors of ancient coins, as soon as I read about the ‘coded series’ of the emperors Probus, Diocletian and Maximian I became intrigued by them. Apart from the short introduction in RIC, there is plenty of information to be found on the net. However, the question what the words mean exactly (or rather, what possible translations can be offered) remains. In this article I will try to give a short survey of several possible translations of the codewords. I will also try to evaluate the evidence pro and con and offer some thoughts of my own.[1]


For the emperor Probus, the word ‘AEQVITI’ appears on four series of antoniniani, struck by the mints of Rome and Ticinum in the years 280-282. Rome spells the codeword ‘AEQVITI’, Ticinum spells ‘AEQVIT’ and ‘EQVITI’.

Figure 1: Antoninianus of Probus from Ticinum’s third officina, code letter EQVITI

In this article I will focus on the translation of the codewords. There is plenty of information to find on the net (see the bibliography) about the composition of the coded series, so I will not go into further detail about that here.

There are two possible roots for the codeword AEQVITI. It can be derived from aequitas (equity, just, fair dealing), or it has something to do with eques (horseman, knight). I will weigh several possible translations, beginning with the least likely.

‘For Aequitas’ (aequitati)

That the codeword derives from aequitas was brought forward as far back as 1873, by the discoverer of the code, Dr. A. Missong (who, by the way, had a collection of 14.000 coins of the emperor Probus). In the publication of his discovery, he explained the words as an abbreviation of the word aequitas in the dative case – aequitati (‘for Aequitas’). Missong thought the word referred to the greater equability and uniformity of the coinage at the time, in regard to the great diversity of dies in the first years of Probus’ reign. It has also been mentioned that this word is found to be associated with the figure of Moneta with scales and cornucopiae and sometimes with the three Monetae. This theory has long been abandoned:

·         Most importantly, the Latin would make no sense: AEQVITI as an abbreviation of aequitati is unlikely at best.

·         If the codeword refers to Aequitas, it would be reasonable to expect the personification of Aequitas (or Moneta for that matter) appearing as a reverse-type on coded coins. This is not the case.

·         The evidence for the second ‘root’ is more compelling, as we will see later on.

Later writers all agree that the codeword, in one way or another derives from eques (‘horseman’) and not from words associated with aequitas.

‘For the Horseman’ (Equiti)

The codewords are all acceptable as the dative case for eques. Or in other words: they can represent the ‘dedicatory’ form of the word. Before I proceed, one remark is necessary here:

·         The word eques (and like wise the dative case equiti), written in flawless Latin would not have the initial ‘a’, the letter we encounter in the spelling of the codeword in both Rome (AEQVITI) and Ticinum (AEQVIT, 1st series). However, this particular phenomenon, called a ‘diphthong’, which is technically a spelling-error, is encountered on other coins of this period.[2] Not very often, but often enough to accept that in this period both equiti and aequiti are valid variants in the spelling of the same word.

But the difficulty remains that eques (and likewise the dative case equiti) can mean a number of things.

The first possible translation of equiti is ‘for the Horseman’. Probus as a horseman. At first glance, this translation will seem very plausible to the collector’s mind, as one of Probus’ most famous reverse-types is ‘the emperor on horseback’.

Figure 2: Antoninianus of Probus from Rome with the emperor on horseback

But as a matter of fact, this type has nothing to do with Probus being a horseman, but has everything to do with Probus’ arrival in Rome in 277 AD. This particular type accompanying the legend ADVENTVS AVG is the traditional numismatic commemoration of this event in the coinage of many an emperor before Probus. Furthermore, being called a ‘horseman’ would not have been very honorable to the emperor’s mind (or to the Roman mind). Consider for comparison the titles Probus is known to have had during his lifetime: ‘good/perpetual imperator’ (bonus/perpetuus imperator), ‘invincible emperor’ (invictus augustus) and last but not least ‘god and lord’ (deus et dominus). Also, ancient sources remain silent about Probus being a horseman. This means the theory that the codewords refer to the emperor as a horseman will need some additional evidence. (And there is! I will return to this topic later on)

‘For the knight’ (Equiti)

The Roman aristocracy was composed of two ranks. The knights (equites) formed the lower part, the senators the upper part. Anyone coming from a family that could boast a consul as a forefather belonged to the senatorial rank. The knights were wealthy Romans without consular forebears. Only if a man of equestrian rank had managed to gain access to the senate (after having been appointed quaestor or consul) he obtained senatorial status. In the time of Probus these ranks still existed, but the strict division was not so clear anymore. The senators had lost their monopoly on the chief magistracies.

I can be short about this possible translation. It is impossible that ‘for the knight’ refers to Probus, because at the time the series were minted, the emperor – already having been consul thrice – technically belonged to the senatorial rank. It is very unlikely someone else was honored by the series. As a rule, only the emperor and members of the imperial family appear on imperial coinage. Also, for the time of the emperor Probus, there appear no candidates for this kind of honor in the ancient sources.

‘For the equestrian order’ (Equiti)

The word eques can also refer to a collective of equites, or in other words: it can refer to ‘all Roman knights’. Along these lines our next possible translation is ‘for the equestrian order’, understanding the coded coins as dedicated to the Roman knights. This does not seem very likely either. There are no precedents for a dedication of coins to the equestrian order and the sources do not mention them as having played a special role during Probus’ reign.

However, the introduction to the coinage of Probus in RIC speculates that the reverse portraying the emperor as princeps juventutis[3] ‘was perhaps an allusion to his close connection with the Equester Ordo’.

Figure 3: Antoninianus depicting the emperor Probus as princeps juventutis

As far as I am concerned there are no grounds whatsoever to assume this:

·         The title princeps juventutis was originally a Republican title, borne by commanders of the equestrian order, mostly young men of senatorial rank. In imperial times the title was bestowed on ‘caesares’, the heirs apparent to the imperial title. In later times we see emperors assume the title (Aurelian was the first) and later still princeps juventutis becomes little more than one of the many honorary titles borne by the emperor. The original connection with the Roman knights is no longer explicit.

·         That Probus ‘mechanically’ assumed the title princeps juventutis when he became emperor is confirmed by numismatic evidence. The antoninianus bearing the legend PRINCIPI IVVENTVT, struck in Ticinum, was minted right after Probus became emperor in 276. Furthermore, this first emission of Ticinum was identical to the last emission of Florian, Probus’ predecessor. Probus just copied Florian’s honorary title along with the rest of his predecessor’s reverses! (Siscia, following the example of Ticinum, struck an aureus bearing this title as a part of its second emission of 277.)

·         There is a gap of three years between the issue of the princeps juventutis-types and the coded series: after Siscia’s aureus the title vanishes from Probus’ coinage. This makes it hard to believe the issues are related to the AEQVITI-series as expressing the same ‘close connection’.

It will be clear that in this author’s opinion the translation ‘for the equestrian order’ does not seem to be very likely.

‘For the cavalry’ (Equiti)

Another collective of horsemen is of course ‘the cavalry’. Along these lines our next possible translation of the codewords is ‘for the cavalry’. This is the first possibility that has something to say for it. Like the introduction in RIC states: ‘It is not unlikely that Probus, whose warlike operations extended over a great area, may also have owed much to the mounted arm, and desired to express that indebtedness.’

As a matter of fact, we have some kind of precedent for this. Another emperor had ‘expressed his indebtedness’ to the cavalry on his coinage a few years earlier. During the reign of Postumus the mint of Milan (possibly under control of Postumus’ commander of the horse Aureolus) issued a series of antoniniani mentioning the mounted forces. We encounter the following reverses: CONCORDIA, FIDES, PAX and VIRTVS EQVITVM.

Figure 4: Antoninianus of Postumus minted at Milan in honor of the cavalry

All these legends are in the nominative case (the harmony of the cavalry – not: ‘for the harmony’). This means the ‘dedicatory’ nature of the series is not apparent right away.

·         It is interesting to see that Postumus’ cavalry-coins show the same errors/variants in the spelling of the word for ‘horsemen’ as our codewords do. There are legends with AEQVIT and AEQVITVM alongside the ones with EQVITVM!

Equitius’ (Equitius)

Theodor Mommsen was the first to identify the codewords as the name Equitius (1887). He writes it is ‘evident’ that Equitius must have been the official in charge of the mint. This theory (or rather: this wild speculation) has not produced any followers, firstly because the series of Rome and Ticinum’s third series are contemporary (both emissions dating 282 AD) which would mean this hypothetical official was in charge of two separate mints at the same time. Secondly, and more importantly, there is a much more likely candidate for the name: one historical source mentions the name Equitius as one of the names of the emperor Probus himself. This source is his Epitome.[4] Karl Pink, the author of the only ‘recent’ study on the coinage of Probus (1949), chooses this name, referring to Probus, as the explanation of the codewords.

Figure 5: ‘Coded’ antoniniani of Probus from Ticinum’s 1st and 2nd officinae with the code letters EQVITI

Equitius is almost certainly a so-called signum: a ‘nickname’. Often, signa were Latin translations of a foreign (Greek or Egyptian) name. This is also the case with the name Equitius. It translates the Greek name Ippius (or Hippios), as becomes clear from an inscription of 245 AD which reads: ‘M IPPIVS … SIGNO EQVITII’ (Translation: Marcus Ippius … with the signum of Equitius’).[5] Above, I stated the theory ‘Probus as a horseman’ would require some extra evidence. Well, here it is: The Greek word Hippios means ‘horseman’.

Before examining the ancient source mentioning Probus’s signum, two remarks are in order on the translation of Equitius:

·         It most probably has nothing to do with Probus being ‘no mean commander of the horse’, as the introduction in RIC states.

·         It also has nothing to do with the, relatively rare, Roman family-name Equitius.

It is a compelling coincidence that the codewords could be referring to Probus’ nickname. But how certain can we be that the emperor really bore this name? First a couple of considerations contra:

·         The signum is found only in the Epitomes (36,2). This is a kind of ‘abbreviation’ of the work De Caesaribus by the ancient historian Aurelius Victor. The date of the Epitomes is unclear, but it will necessarily have to be after Victor published his work in about 360 AD.

·         The anonymous author of the Epitomes used other sources in addition to Victor’s work. His main interest was biography (i.e. gossip). His reputation for reliability is not particularly high (as is the case with all of the written sources dealing with Probus).

·         All this means that the signum is absent in all other known (and earlier) written sources. Aurelius Victor’s ‘original work’ does not mention the name, nor does the writer of ProbusVita in the Historia Augusta. Zosimus, a Greek historian writing in the fifth centery AD does not mention the signum either.

·         More importantly: not a single coin or inscription calls Probus Equitius.[6]

I stated above that the ancient sources do not mention Probus as being a horseman. There is, however, a story in the Historia Augusta relating how Probus, when he was serving as a general under the emperor Aurelian, acquired a famous horse. This story may have some sort of connection with his nickname. Here it is:

‘Once, indeed, when a horse was found among the booty … which, though not handsome or especially large, was reputed … to be able to run one hundred miles in a day and to continue for eight or ten days, all supposed that Probus would keep such a beast for himself. But first he remarked, “This horse is better suited to a soldier who flees than to one who fights,” and then he ordered the men to put their names into an urn, that the one drawn by lot should receive the horse. Then, since there were in the army four other soldiers named Probus, it so chanced that the name of Probus appeared on the lot that first came forth, though the general’s name had not been put into the urn. And when the four soldiers strove with one another, each maintaining that the lot was his, he ordered the urn to be shaken a second time. But a second time, too, the name of Probus came forth; and when it was done for the third and the fourth time, on the fourth time also there leaped forth the name of Probus. Then the entire army set apart that horse for Probus their general, and even those very soldiers whose names had come forth from the urn desired it thus.’

It is possible that Probussignum gave rise to the fabrication of this legendary story. There are many examples of stories explaining names and situations to be found in ancient myth and historiography. This could well be another one. It explains how the emperor got his wonder-horse and also why he can be called Equitius. It also deals with the problem that being called a ‘horseman’ is not particularly honorable. Probus is hesitant at first to accept even a wonder-horse. Later he does accept it, but only after it is made very clear that it is ‘supposed to be’.

More compelling evidence for understanding the codewords as referring to Probussignum comes in the guise of the coded series of Diocleatian and Maximian. These emperors, as we will see, may have also put their nicknames on coded coins. But first the question is: in what way does the name Equitius appear on the coded coins?

The first possibiltity is that the mints of Rome and Ticinum just abbreviated the name in the normal, nominative form: ‘Equitius’. The length of the abbreviation is confined by the number of officinae in both mints: Rome had seven officinae, Ticinum had six. For this reason the name was abbreviated to seven and six letters. We encounter (A)EQVITI[VS], without ‘VS’, and, in the case of Ticinum’s first series, AEQVIT[IVS] without ‘IVS’). Maybe if Ticinum had had eight offinae, I would now have been discussing the EQVITIVS-series.

‘Of/Belonging to Equitius’ (Equitii)

Karl Pink, the author of the only extensive study on Probus’ coinage chooses another translation. He explains the codewords as the name Equitius appearing in the genitive case.[7]

And indeed, our codewords are all acceptable as the genitive case of the name Equitius: (‘Of/Belonging to Equitius’) after we consider the following:

·         The additional ‘a’ in the codewords can be seen as a variant in spelling (see the remark on the ‘diphthong’ above).

·         The genitive case in flawless Latin would read Equitii, with an extra ‘i’. Probably because the ancient Romans did not pronounce the second ‘i’, this letter is omitted on a regular basis in written texts (likewise fili instead of filii).

However, the use of genitive cases for names of emperors is more problematic than Pink makes it appear in his article. I will return to this matter later on.


Approximately a decade after Probus’ coded series, the Siscia mint produced a few series of coded antoniniani for the emperors Diocletian and Maximian (see the article by Chip Scoppa). In the exergues of the coins of Diocletian we encounter the word IOBI split up three-way (I, O and BI) and likewise for Maximian the word HPKOYΛI (HP, KOY, and ΛI).

Figure 6: Antoninianus of Diocletian from Siscia’s third officin with the code letters IOBI

·         It is peculiar that these words, which are clearly Latin, appear in Greek lettering. (The words derive from ‘Jupiter’ and ‘Hercules’, not from their Greek counterparts Zeus and Herakles).

·         It is even more peculiar that (maybe) the Latin grammatical decline also appears in Greek lettering! This phenomenon, however, (the transliteration of foreign words, including grammatical decline, into another language) is not unique and can be found in inscriptions also.

But what can these words mean? The first possibility, as stated above, is that they represent the nicknames of the emperors in question.

Jovius’, ‘Herculius’ (Iovius and Herculius)

At the time the coded series were minted, the empire was ruled by Diocletian in the east and Maximian as his co-ruler in the west. As a part of the reorganization of the Empire, the emperors established an emperor-cult on a scale that had not existed earlier. Diocletian, the senior Augustus, presented himself as the manifestation of Jupiter, while Maximian was to be seen as Hercules made flesh. It is well-known to collectors that Maximian went very far in identifying himself with his patron deity (as can be seen on the coins portraying him with a lion skin) and that he assumed the name Herculius. Not so well-known is the fact that Diocletian, on the other hand, assumed the name Jovius. By assuming these names, which are modifications of the names of the patron deities, the emperors implied having a close connection to these particular gods.

Joseph van Kolb, the man who must be credited with the discovery of the codewords in 1872, states that the codewords refer to these nicknames.[8]

There are two ways in which the names can be appearing on the coins. Like it is the case with Equitius (see above), the codewords can be the emperors’ nicknames in the abbreviated nominative case: IOVI[VS] and HERCULI[VS]. But, considering there was enough space to put ‘KOY’ in the exergue of the second coin, why abbreviate at all?

It remains a noteworthy coincidence that: 1) all of the codewords can be understood as referring to the nicknames of the three emperors and 2) the manner of abbreviation is apparently the same: in all the codewords the last syllable – us – of the names Equitius, Jovius and Herculius is omitted.

‘Of/Belonging to Jovius, Of/Belonging to Herculius’ (Iovii and Herculii)

The codewords are also acceptable as the genitive form of those nicknames (see the remark on the extra letter ‘i’ in the section ‘Of/belonging to Equitius’). This gives the translation ‘Of/Belonging to Jovius’ and ‘Of/Belonging to Herculius’. Our codewords appear in this way on a silver medaillon of Diocletian and Maximian bearing the legend MONETA IOVI ET HERCVLI AVGG – ‘coin of the emperors Jovius and Herculius’.

Figure 7: Antoninianus of Maximian from Siscia’s second officina with the code letters HPKOYΛI

‘For Jupiter, For Hercules’ (Iovi and Herculi)

As a final possibility, the codewords may represent the dative case of the names Jupiter and Hercules. This way we get the translation ‘for Jupiter’ and ‘for Hercules’ and the coins are understood as ‘dedicated’ to those deities. There are numerous examples of coins ‘dedicated’ to the gods, which is often clear because their names appear in ‘dedicatory form’, i.e. the dative case. In the coinage of Diocletian and Maximian we see examples of this in legends like IOVI CONSERVATORI AVGG (‘for Jupiter, protector of the emperors’) and HERCULI PACIFERO (‘For Hercules the peace maker’) – note that the words used in these legends are also our codewords.

III - Conclusion

Considering all these possible translations, two lines of interpretation remain, as far as I am concerned. Either the codewords are a rendition of the three emperor’s nicknames or they are to be understood as dedications: in the case of the AEQVITI-series to the cavalry, in the case of IOBI and HPKOYΛI to Jupiter and Hercules.

However, the thing that bothers me about Pink’s version of the nickname-theory, is that the names would have to appear in the genitive case:

·         In the whole history of Roman imperial coinage we never encounter a name of an emperor in the genetive case by itself.[9] Names appear either in the nominative case (IMP PROBVS AVG – ‘the emperor Probus’) or in the dative case (IMP PROBO AVG – ‘dedicated to the emperor Probus’). A genitive case never appears in isolated form, but is always accompanied by a word requiring it (VIRTVS PROBI AVG ‘the courage of the emperor Probus, see also the legend on the medaillon quoted above).

·         So: if the codewords really are the nicknames of the emperors in the genitive case (expressing that the coins ‘belong to the emperor’[10]), the mints of Rome, Ticinum and Siscia would be running against three centuries of numismatic convention and tradition. Pink (1949) does not really explain this problem, nor does Colombetti (1989), who just reiterates Pink’s interpretation. Pink takes the appearance of the signa in the genitive case for granted but the case for this reading is not as clear-cut as he makes it appear.

·         If Probussignum was put on the coins, it is much more probable that a dative case (Equitio) or a nominative case (Equitius) would have been used. Considering the fact that, as stated above, the words can be understood as the nominative case in abbreviated form, why choose the more problematic reading?

IV – Epilogue: Who would notice?

Trying to make sense of a code is a dangerous undertaking. A code, by nature, is not meant to be understood by outsiders. Consider the Siscian coins of Diocletian and Maximian: the codewords are, as stated above, Greek translitterations of Latin names, maybe even including the Latin grammatical decline. This is very strange, considering the fact that Siscia was a part of the Latin-speaking region of the Roman Empire.

Doug Smith, in an email to this author, remarks: ‘In general, I would see use of Greek letters in a Latin region (or vice-versa) as a sign that the code was not intended to be read by anyone outside the mint. This is rather like the pull date codes used in grocery stores. They don’t want you to know when it was packaged.’

It all comes down to common sense, really. Imagine the chances for an average citizen of Roman Siscia to: 1) be able to read, 2) be able to read Greek, 3) of all the coins in circulation get his hands on three different coded coins of the same emperor, 4) study the reverses close enough to notice the letters in the exergue at all, and 5) discover that some letters in the exergue of three particular coins – read one after another in the right order – spell out a word. I think the odds will be against him.

The same line of thought applies to the AEQVITI-series: the chances for ‘the average man’ actually noticing the codeword are very slim. These considerations shed some doubt on the explanation that with the series, the emperor Probus desired to ‘express his indebtedness to the mounted arm’. A code that would not have been noticed by almost everybody is a very peculiar way to do that.

It is reasonable to assume, in my opinion at least, that the meaning (and perhaps even the existence) of the coded coins was known only to the workers and officials at the mints. Perhaps the letters were nothing more than control marks. These control marks are encountered frequently on Roman coins, their purpose being probably to enable the mint workers to distinguish between the different emissions. Usually these control marks do not have a deeper meaning, but in the present case several of them spell out a word. About the question why the officials at the mints of Rome, Ticinum and Siscia chose these particular words, we will probably never be sure.


Colombetti, Luigi, ‘Cenni sulla monetazione di Probo gli antoniniani delle serie (A) EQVIT (I) (zecche de Roma e Ticinvm).’ La numismatica 20, 11 (1989) p. 339-340.

Dannhäuser, Erich, Untersuchungen zur Geschichte des Kaisers Probus (276-282).
(Inaugural Dissertation) 1909.

Kolb, Joseph von, ‘Enträthselte Siglen auf Münzen Diocletians and Maximians Numismatische Zeitschrift (1872) p. 24-30.*

Kolb, Joseph von, ‘Enträthselte Siglen auf Münzen Diocletians and Maximians Numismatische Zeitschrift (1873) p. 116-121.

Missong, A, ‘Gleichartig systemisirte Münzreihen unter Kaiser Probus’, Numismatische Zeitschrift (1873) 102-115.*

Mommsen, TheodorEquitius.’, Zeitschrift für Numismatik, 15 (1887) p. 251-252.

Mowat, R, ‘Combinaisons secrète de lettres dans les marges monétaires de l’empire Romain’, Revue Numismatique, 1897 67-81.

Pink, Karl, ‘Der Aufbau der römischen Münzprägung in der Kaiserzeit. VI/I, Probus.’,
Numismatische Zeitschrift
73 (1949), p. 13-74.

Real-Encyclopädie der klassischen Altertumswissenschaft: lemma ‘Aurelius’, ‘Equitius’, ‘Signum’.

Roman Imperial Coinage volume V part II.

* The articles announcing the discovery of the coded coins.

Worthy of mention are the following web pages:

Chip Scoppa’s overview of the coded coins of Probus and his fascinating article based on the ‘Siscia mule’:

Doug Smith’s pages on the coded series: 

A comprehensive site of the coinage of Probus worth visiting:

This article can also be read on at the following link:

[1] I would like to thank Chip Scoppa and Doug Smith for their comments and for taking the time reviewing my work. Also I would like to thank Dick Boersema, Virtvsprobi, Bob Vuijk, Sylviane Estiot and Curtis Clay for their help.

[2] We find PIAETAS as well as PIETAS, SECVLI alongside SAECVLI, and on coins of Postumus, minted only a few years earlier, the word EQVITVM, which is also derived from our ‘root’-word eques, is sometimes spelled AEQVITVM.

[3] On two coins: An antoninianus of Ticinum (RIC 318) and an aureus of Siscia (RIC 892).

[4] Epit. de Caes. 36,2 reads: ‘Sed, cum magna pars exercitus Equitium Probum, militiae peritum legisset, Florianus...’

[5] CIL III 2706 reads: ‘M. Ipp[ius] L. f. Stel(latina tribu) Benevento Vitalis, (centurio) coh(ortis) VIII vol(oluntariorum), - - sig(no) Equitii.

[6] So either 1) the signum has its origin in an ancient source, known by the author of the Epitomes, but unknown to us, or 2) the signum is a fabrication of the Epitomizer, or 3) the signum is the result of a copying-error (for ‘Aurelium’ perhaps) in the surviving manuscripts of the Epitomes. It is of course possible the name will occur in some future discovery. According to Dannhäuser Equitius Probus was the name Probus bore before assuming the name Marcus Aurelius Probus when he became emperor (1909 p.13/14 note). This would explain why the name doesn’t appear on his coinage.

[7] In the most recent publication on the subject, Colombetti (1989) reiterates Pink’s interpretation.

[8] Von Kolb, in his article (1872) announcing his interesting discovery, writes that his curiosity was captured by the long, strange string of letters (‘BXXIKOY’) in the exergue of a coin of Maximian. He found out the about the coded series after studying the Vienese collection. It is interesting to see that Missong published his discovery of the codes on Probus’ coins only one year later.

[9] I could find one example on Doug Smith’s site. A Siscian bronze of Constans as caesar bearing the legend FL CONSTANTIS BEA C (RIC VII 238 - Siscia).

[10] This is the most probable explanion of the ‘isolated’ genetive case in which names of rulers appear on Greek coins.