Thanks for everyone's comments!
As
Curtis notes, the coin
type barely even hints (only by way of being a special
type, and issued by
Maxentius) at the special relationships behind it, but there are a few other hints from the other coins exchanged at the time.
In addition to this
PERPETVA VIRTVS for
Constantine as
Caesar,
Maxentius also issued
VIRTVS PERPETVA AVG for
Constantine as
Augustus, depicting either
Hercules wrestling the
Nemean lion, or (per
Failmezger - I've never seen one) Virtvs as on the first coin. The significance of Constantine's title of
Augustus, highlighted by both the
reverse legend and the fact that's it's a
legend variant of the earlier
type as
Caesar, is that this came about by
Maximianus (as
part of the deal) having reacclaimed him as such after
Constantine had earlier accepted demotion by
Galerius to
Caesar after
his initial acclamation as
Augustus by
his father. Again it's only the
contemporary sources that supply this information, but the coin pairing does confirm the new title being
part of the occasion of issuance of these special
types. The Herculean reference seems to suggest acknowledgement of Constantine's legitimate succession into the Western house, both from
his father as well as from
Maximian, despite
Maxentius having also
had himself declared as a Western
Augustus.
Continuing on the theme of Virtvs,
Maxentius also issued
VIRTVS CONSTANTINI CAES for
Constantine as
Caesar, with two alternate
military themed designs, and this being a special
type and the Constantinian
legend both hint at the special relationship rather than a routine acknowledgement of a co-ruler.
The
choice of VIRTVS as the theme for these coins, which perhaps seems rather cold given the family tie, should probably be taken to confirm the significance of Maximianus's deal with
Constantine being seen purely as political/military, with
Fausta merely being used as a pawn. Indeed she may have been as young as 9 at the time (her date of birth is uncertain, and an upper bound on her age is ~18), which would explain why she would not bear
Constantine children for another 9 years. VIRTVS also appears to have been the bon mots du jour between imperators, as
Severus had the year earlier issued
VIRTVS AVGG ET CAESS NN to recognize the new Caesars.
As a more direct numismatic reference to the circular family relationships, there's
HERCVLI CONSERVATORI issued by
Constantine from
London in 307 for
Maximianus, which (Maximainus not having control over any mints) seems to have been
met with HERVCLI CONSERVAT CAES issued by
Maxentius for
Constantine, again with the Western/family
Hercules and
Nemean lion motif.
Finally we also have the
Constantine issued
PLVRA NATAL FEL and
MVLT NATAL FEL Trier fractions, the former issued for
Maximianus as well as
Constantine, which ("Many happy births") is the only halfway direct recognition of Constantine's marriage to Maximianus's daughter.
As for the asymmetry of the numismatic recognition between
Constantine and
Maxentius,
Maxentius issued both these special
types for
Constantine as well as
his normal
types in reasonable quantity, while
Constantine had only responded with (as far as I'm aware)
his normal
MARTI PATRI CONSERVATORI (Trier?) and
GENIO POP ROM (Lyons)
types in excruciatingly small quantity. I think this asymmetry reflects two things - first that
Maxentius was a usurper with little support while
Constantine was a legitimate Western
Augustus (having been acclaimed first by
Constantius I, acknowledged as
Caesar by
Galerius, then reacclaimed
Augustus by
Maximianus).
Maxentius appears to have been hoping, and numismatically begging, for the family tie to encourage Constantine's support, while Constantine's cool response from a position of power perhaps signalled
his early ambitious intentions (as noted in the
contemporary sources) from the start. Secondly,
Constantine very rapidly became hostile to
Maxentius as the latter took control of
Spain which
had been Constantine's territory.
I'm currently reading the
contemporary sources available in translation for
Constantine, and shall try to compile a list of notable differences between them such as the precise means of Fausta's end (at least it seems to have been at bathtime!). There are many interesting details in these sources, some of which contradict the common abridged version of events. For example, it turns out that it was not the Milvian bridge itself that collapsed, causing
Maxentius to drown, but rather a pontoon bridge of boats that
Maxentius had constructed (having destroyed the permanent bridge), which he'd hoped to become Constantine's demise by way of a quick-detach device he'd fashioned to split the bridge at some opportune time.
Ben