Antoninianus - Probus Cuirassed, left, spear and shield, from behind; FIDES MILIT; Fides

Reverse

Fides, draped, standing left, holding ensign in each hand.

Script: Latin

Lettering:
FIDES MILIT
In exergue: mark of the 6th officina (VI), followed by value mark (XX) and mint mark for Ticinum (T)

Unabridged legend: Fides Militum.

Translation: Loyalty of the soldiers.

Comment

RIC 366 was minted by the 6th officina (exergue-/officina mark: VIXXT) of the Ticinum mint (VIXXT). The XX stands for 20 parts alloy (instead of the more usual XXI for a copper to silver ratio of 20:1). The original RIC text mentions 3 different variations/different bust types (bust types according to Pierre Bastiens grouping of bust types; see illustrated: probvs.net), and there are also multiple variants known:

1. Helmeted, radiate, cuirassed, left, holding spear in right hand and shield in left hand (E1 bust, example probuscoins #987, Numista #292714);
2. Helmeted, radiate, cuirassed, left, holding spear in right hand and shield in left hand, from behind (E2 bust, example probuscoins #2603, Numista #413544);
3. Radiate, cuirassed, left, holding spear in right hand and shield in left hand (F1 bust, example probuscoins #4232, Numista #293485);
4. [var] Radiate, cuirassed, left, holding spear in right hand and shield in left hand, from behind (F8 bust, example probuscoins #1160, Numista #413545);
5. [var] Radiate, heroically nude, left, holding spear in right hand and square shield (Aegis) in left hand, from behind (F19 bust, example probuscoins #3741, Numista #413546);
6. [var] Helmeted, radiate, heroically nude, left, holding spear in right hand and square shield (Aegis) in left hand, from behind (E8 bust, example probuscoins #1706, not in Numista);
7. [var] Radiate, cuirassed, left, holding spear in right hand (F5 bust, example probuscoins #342, not in Numista).

According to Pink, RIC 366 - with its obverse lettering nr. 4 ('VIRTVS PROBI AVG') combined with 'FIDES MILIT' - is part of the 3rd emission (the year 277) and 4th emission (278) (Karl Pink, Der Aufbau der römischen Münzprägung in der Kaiserzeit VI/I, Wien, 1949, p. 61-63).

About the F19 and E8 variants

The only difference between the F19 and E8 bust is that the E8 bust is helmeted. The F19 and E8 bust are not in RIC at all. RIC sometimes mentions a 'square shield' (for example: RIC 388) or even an 'aegis' (for example: RIC 296), however it always mentions Probus 'cuirassed' while the F19 and E8 bust are '(heroically) nude'.

Interesting fact