The lion can be a personification of Africa, or a symbol of Herakles, the Empire, Providence or Fortitude.

Doug Smith's Lions on Coins Page - 

Dictionary of Roman Coins

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Lion - The lion appears in the attitude of walking on coins of Mark Antony, Antoninus Pius, Caracalla, Philip I, Gallienus, Aurelian, Probus, and other emperors. In this attitude he is also the |symbol| of imperial consecration, see MEMORIAE AETERNAE; likewise of munificence, see MVNIFICENTIA - SAECVLARES AVG.

A lion with a thunderbolt in his mouth is

seen on coins of Caracalla, Aurelian, Postumus, Probus, and Diocletian.

He stands at the feet of Hercules in a brass medallion of Hadrian, and at the feet of Cybele (see MATRI DEVM), who is also seated with a lion. On account of the abundance of these |animals| in that quarter of the globe, Africa is personified, having likewise a lion at her feet on coins of Hadrian, Commodus, and Diocletian. A biga of lions, with the legend AETERNITAS, is the type of consecration.

A lion pierced with a lance, which the emperor on horseback holds in his hand, is seen on a coin of Commodus, with the legend VIRTVTI AVGVSTI. On a first brass of Hadrian, the emperor is striking his dart at a lion running before him, with the legend VIRTVS AVGVST. On a silver medal of Constantine the Great is the same type; see LIBERATOR ORBIS.

A lion fighting with a stag, which it is tearing to pieces, appears on a coin of Augustus, struck in memory of a grand hunting of wild beasts, instituted in celebration of that emperor's birthday. See Durmia gens.

A lion and boar yoked together to a chariot in which Victory is seated, and before which Hercules marches, is given by Havercamp among the Contorniate medals of Trajan. On a coin of the same emperor, four lions draw a car in which are Trajan and Plotina.

The lion is the sign of Fortitude. Hence we see him on a coin of Gallenius as the accompanying type of LEG IIII FL. By the same rule the lion is the |symbol| of Hercules, and of Herculean labour and fortitude. Represented with radiated head, and with the thunderbolt between his teeth, as on coins of Caracalla, Severus Alexander, Probus, Maximianus, and other emperors, the lion is the acknowledged |symbol| of empire and of providence.

On an elegant gold coin of Gallienus in the Imperial Cabinet at Vienna, the type of a lion with an eagle on its back appears within a crown of laurel, and below are the initial letters S P Q R.

The lion's skin is seen on the head of some Roman emperors, such as Commodus, Severus Alexander, and others; also, more rarely, on the head of Gallienus.

[Greek coinage of Alexander the Great often represents the head of Herakles (Hercules) wearing a lion-skin headdress]

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