Postumus Double Double Sestertius

John Conduitt · September 17, 2023

This is a strange coin, struck when Postumus was trying to strengthen the currency against inflation at the start of the Gallic Empire. It’s a denomination first struck by Trajan Decius but revived by Postumus. It’s now known as a double sestertius, since it was larger than the sestertius (but not double) and featured a radiate crown, the Roman way of indicating double value without putting twice as much precious metal into the coin.

What makes it stranger is that he struck many of these over Antonine sestertii, which had been circulating for over 100 years. The overstriking was often so poor that the under-coin was clearer than the overstrike. Here the reverse appears to be Pietas, but Pietas didn’t feature on Postumus’s bronze coins. The S C shouldn’t be there either, given Postumus had no senate to approve his coins, although some of his coins did seem to have it. The reverse instead comes from Faustina I, whose outline seems to sit behind Postumus on the obverse.

Postumus Sestertius, 261-262

Cologne. Bronze, 32mm, 23.61g. Bust of Postumus, radiate, draped, cuirassed, right; IMP C M CASS LAT POSTV(MVS P F AVG). Unknown reverse, possibly Felicitas, draped, standing left, holding caduceus in right hand and cornucopia in left hand; FELICITAS PVBLICA (RIC V, 122). Found in Essex.
Overstruck on: Faustina I Sestertius, 141. Rome. (Average size 29-32mm, 23.5g). Bust of Faustina I, draped, right, hair elaborately waved and coiled in bands across head and drawn up at back and piled in a round coil on top; DIVA FAVSTINA. Pietas, veiled, draped, standing left, raising right hand above lighted altar left and holding box in left hand; AVGVSTA S C (RIC III, 1127).

Working out which coins created the reverse isn’t easy, since it isn’t clear which letters are from the over or under-coin. I can see the letters that would form AVGVSTA S C from the Faustina coin, but what’s left doesn’t seem to form anything else. The combination looks like AAV(GV)CTAVG. But the many As are not in the right places – either of the two at the start could be from AVGVSTA, leaving a spare, while the other A seems too close to Pietas to be the last A, even though it does follow T. Postumus’s double sestertii are known to have borrowed reverses from Trajan Decius and that included FELICITAS PVBLICA, which is what I’ve used here for the over-coin. An example can be found here, although it’s only 16.5g.

Nor is the mint certain. I’ve said Cologne, but the references still talk about Lugdunum (not now seen as a Gallic Empire mint). This second Gallic Empire mint (that isn’t Trier) is sometimes called Mint II or an Irregular Mint, although that might include barbarous issues. The reason this is assigned to Cologne is the bust (like the example linked above), although it has become grotesque in the overstriking process.

Conversely, the dating is very precise. The legend IMP C M CASS LAT POSTVMVS P F AVG contains his full name, so should be the earliest coinage, but the reverse types and the fact that they spelled his name correctly (unlike on the early silver) put these double sestertii a bit later in Postumus’s third coinage. Apparently, production of the double sestertii ceased in 262 (perhaps since they needed the bronze to make antoniniani) so that creates a narrow window. The size of the coins reduced from 25g to 20g over this time, putting my coin towards the start of the range. Even so, the double sestertius circulated until the late 260s and spawned many imitations before it finally disappeared.