For the image: http://numismatics.org/ocre/id/ric.6.nic.5a

RIC VI, Nicomedia, no. 5a, p. 554.

This aureus, minted in 294 CE at Nicomedia, depicts on the obverse the head of Diocletian, and on the reverse Jupiter holding a sceptre and a thunderbolt (a symbol traditionally associated with him). The inscription on the obverse refers to the emperor, as Diocletian, Pius, Felix (or dutiful), and Augustus. The title Augustus served to emphasize the emperor’s sacral standing, but it also indicates his primacy in the tetrarchy established the previous year in 293 CE. Replacing the former Dyarchy which saw Diocletian and Maximian reign as co-Augusti, the tetrarchy saw four emperors sharing rule of the empire, with Diocletian and Maximian as Augusti and Galerius and Constantius I (Constantius Chlorus) as Caesares. The inscription on the reverse refers to Jupiter as Conservator, or the keeper of the Roman state. The inscription in the exergue, SMN, indicates that the coin was minted at Nicomedia, the main residence of Diocletian from 286 CE onwards.

The depiction of Jupiter on the reverse indicates that Diocletian had reverted to the traditional cult of the Roman state, embodied by Jupiter. During the rule of one of Diocletian’s predecessors, Aurelianus, the solar god, Sol Invictus, had displaced Jupiter as the supreme god of the Roman state. Jupiter was traditionally the main god of Rome and he was identified with the senatorial class. The main temple in Rome on the Capitoline Hill was dedicated to Jupiter, together with the two other members of the Capitoline Triad, Juno and Minerva. However, during his reign Diocletian revived the cult of Jupiter along with the cult of Hercules, and proceeded to closely associate the two gods with the government of him and Maximian (his fellow Augustus). Erika Manders notes that coin types featuring Jupiter became popular in the Tetrarchic period due to Jupiter being once again assigned the highest place in the Roman pantheon, and the practice of associating the senior emperors with him. As such Jupiter featured most prominently on Diocletian’s coins (Coining Images of Power, p. 104; see also Rees, Diocletian and the Tetrarchy, p. 54; Noreña, Imperial Ideals, p. 342 lists 297 coins of Diocletian which feature Jupiter). Just as Jupiter had overthrown the old Titan race and ruled over the new and superior Olympians, Diocletian represented himself to be presiding over a new age of the Roman empire during which the unstable period of usurpation that had preceded would be no more (see Williams, Diocletian and the Roman Recovery, p. 58).

The inscription on the reverse of this coin refers to Jupiter as conservator, one of his key attributes. This identifies Jupiter as preserver and protector. The pairing on the coin of Diocletian with Jupiter as the preserver therefore served to suggest that the emperor, who ruled over the oikoumenè, was in fact a reflection and representative of the supreme god who reigned in the heavens. The present coin forwards the message that both Jupiter and his earthly agent, the emperor, are protecting the empire together.

Moreover, the depiction of Jupiter served also to mirror the relationship between the two members of the Dyarchy, Diocletian and Maximian. In 287 CE Diocletian assumed the title Iovius (i.e. Jupiter), and his partner Maximian assumed that of Herculius (i.e. Hercules), who was the last earthly son of Jupiter. The title Iovius clearly indicated Diocletian’s supremacy and his task as planner and organizer, while the title Herculius indicated a subordinate position, but also an active role as military commander (on the claiming of the titles Iovius and Herculius, which would later extend to the other members of the Tetrarchy, see, for instance, Rees, “The Emperors’ New Names”; Kolb, Diocletian und die Erste Tetrarchie, p. 88-114). Divine patronage was something which gave their rule legitimacy (Williams, Diocletian and the Roman Recovery, p. 59). By presenting themselves as the sons of Jupiter and Hercules, Diocletian and Maximian were able to claim a divine source for their imperial power. By the time this coin was minted, then, Diocletian was presenting himself as consecrated by the gods and possessing of a sacral standing. Therefore, this issue essentially emphasizes the sacral role of the ruler of Rome, agent of the supreme god, who has taken on the duty of protector and preserver of Rome that Jupiter was responsible for. Just as Jupiter had ushered in a new age of stability following unrest, Diocletian was doing the same.