Carus, 282-284, had two sons, Carinus and Numerian, who became emperors. In September I announced an educational webpage on their coins and how the number of Gs in "AVGGG" helps determine the date of the coin: http://augustuscoins.com/ed/Carus/ I have added a Carus with three G's to the page. Carus. 3.88 grams. 21-20 mm. IMP C M AVR CARVS PF AVG VIRTVS AVGGG (three Gs for three rulers) * Δ XXI RIC V.II Carus 125, Antioch mint, page 150, Plate VI.17 The sequence of events leading up to there being three simultaneous rulers is 1) Carus became emperor at the end of August 282 2) Carus elevated Carinus to Caesar in autumn 282 After this point in time reverse legends that would have had "AVG" with one ruler change to have the plural form "AVGG" 3) Numerian was made Caesar late autumn 282 After this point in time reverse legends that would have had "AVGG" can have "AVGGG" with three Gs for three rulers, but that change actually happened only at Antioch (the location of their promotion); the rest of the mints retained AVGG. Coins of Carus with AVGGG that may belong to this period might also belong to the next because they continue unchanged into the next period. The next event changes the obverses of coins of Carinus and Numerian. 4) Carinus and Numerian were promoted to Augustus February/March 283 After this point in time their obverse legends change from CAES to AVG, but the reverse number of Gs does not change. 5) Carus dies c. autumn 283 After this point in time legends of Carinus and Numerian revert to AVGG, with only two Gs for the two remaining rulers. So the date of this coin is "late autumn 282 to c. autumn 283." I think it is neat that we can have a coin over 1700 years old that can be dated to within a year. There is more on the page. http://augustuscoins.com/ed/Carus/ Show us anything related!
I believe it's similar with Carausius. He started off with just the one G, trying to establish himself as sole emperor of the Britannic Empire, but later added 2 more Gs for Diocletian and Maximian in the hope of being recognised as co-ruler. None of these tricks made any difference to his fortunes. Thanks for giving me the chance to post this coin again Diocletian (struck under Carausius), 292-293, London. 4.34g. Pax Antoninianus. IMP C DIOCLETIANVS P F AVG. PAX AVGGG; S - P in fields, mintmark MLXXI (RIC V, ii, p.552, 9). The dates came from the auction house. I've also seen it listed as '291AD' exactly. Maximian (struck under Carausius), 286-293, London. 22mm, 4.29g. IMP C MAXIMIANVS PF AVG. PAX AVGGG, S-P (RIC V 34). Presumably, this was also later in his reign (the dates quoted are Carausius's whole reign). Again, I've seen it listed as 291AD.
To me, the unusual part was the use of a G to indicate not only the Augusti but also the Caesars making possible coins of a Caesar like this Numerian with AVGGG reverse.
I have no G's and the reverse of this Carus, which I believe is from his sole reign (Thanks to @Valentinian for the correction): Carus, silvered Ӕ Antoninianus, Siscia, AD 282-283 Obv: IMP C M AVR CARVS P F AVG, radiate and cuirassed bust right Rev: RESTITVT ORBIS, female standing right, presenting wreath to emperor, standing left holding globe and scepter; star above P between, XXI in exergue Ref: RIC 106
If the reverse legend on a coin of Carus does not end AVG, AVGG, or AVGG, as that one does not, there are no simple chronological indicators on the coin. However, it is possible for the mint- and field-mark sequence to add information. RIC (published very long ago in 1933) attributes that combination to Siscia and does not put the Siscia mintmarks in order, so the coin is dated to the entire length of his reign, which would include the time period when his sons were co-rulers. If research since then has put them in order and dated them more precisely, I'd like to learn about it.
