Antoninianus - Probus Imperial mantle, left, sceptre surmounted by eagle; CONCORDIA MILIT[VM]; Concordia

Reverse

Probus, standing right, clasping hand of Concordia, standing left.
Sometimes officina mark in field.
Value (XXI) and officina mark in exergue.

Script: Latin

Lettering:
CONCORDIA MILIT or
CONCORDIA MILITVM

Unabridged legend: Concordia Militum.

Translation: Harmony with the soldiers.

Comment

RIC 666 was minted by the Siscia mint. The original RIC text lists 4 variations/different bust types (bust types according to Pierre Bastiens grouping of bust types; see illustrated: probvs.net) and, there is one variant known: 

1. Radiate, draped, right (A bust, Alföldi (*) 023.036-040 (example: probuscoins.fr #1543), Numista #293022);
2. Radiate, draped and cuirassed, right (A2 bust, Alföldi 023.041-053 (example: probuscoins.fr #2936), Numista #293684);
3. Radiate, cuirassed, right (B bust, Alföldi 023.062-079 (example: probuscoins.fr #421), Numista #293688);
4. Helmeted, radiate, cuirassed, left, holding spear in right hand and shield in left hand (E1 bust, Alföldi 023.081-092 (example: probuscoins.fr #3714), Numista #293686);
5. Radiate, wearing imperial mantle, left, holding sceptre surmounted by eagle in right hand (H2 bust, Alföldi 023.015-035 (example: probuscoins.fr #4946), Numista #293687);
6. Radiate, cuirassed, left (B1 bust (**), Alföldi 023.054-061 (example: probuscoins.fr #4257), Numista #293685);
7. [var] Helmeted, radiate, cuirassed, left, holding spear in right hand and shield in left hand, from behind (E2 bust, Alföldi 023.093-094 (example: probuscoins.fr #3612), not in Numista);
8. [var] Radiate, cuirassed, left, holding spear in right hand (F5 bust, Alföldi 023.080 (example: probuscoins.fr #120), not in Numista);
9. [var] Radiate, wearing imperial mantle, left (H bust, Alföldi 023.016-024 (example: probuscoins.fr #1479), not in Numista);

(*) Andreas Alföldi, Vorarbeiten zu einem Corpus der in Siscia geprägten römischen Kaisermünzen. Heft V. Verzeichnis der Antoniniane des Kaisers Probus, Budapest, 1939).

(**) RIC lists “cuirassed bust without weapons” with “left” being omitted by mistake. The B1 bust does not have its own letter in RIC and is therefore fully written out in this way each time. See, for example, RIC 699 (Numista #293726). The B1 bust, commonly listed as a variant for RIC 666, is therefore not really a variant.

RIC lists that the reverse legend can be ‘CONCORDIA MILIT’ or ‘CONCORDIA MILITVM’. The last mentioned legend however is not once listed by Alföldi and no examples of this legend for Siscia have been published (see for examples: Cyzicus and Serdica) so this listing is most likely a mistake. 

According to Pink, RIC 666 – with its obverse lettering nr. 8 (‘IMP PROBVS P F AVG’) combined with “CONCORDIA MILIT K. u. Conc.” (Emperor and Concordia) – is part of the 6^th emission (exergue-/field mark style: -//PXXI; year 279) and 7^th emission (P//XXI; 280). See: Karl Pink, Der Aufbau der römischen Münzprägung in der Kaiserzeit VI/I, Wien, 1949, p. 40-41. 

Note that probuscoins.fr currently attributes two coins with reverse legend ‘CONCORDIA MILIT’ mistakenly to RIC 653 which is an entry for ‘CONCORD MILIT’: #4315 (B1 bust, also listed for RIC 666 as #4257) and; #1619 (E1 bust).

Interesting fact