What a great yet puzzling find!
Yes, this is an imitation of a
solidus of
Constantine IV (Class III in the
Dumbarton Oaks Catalog). The reference
mint would be
Carthage, the
diameter and lack of
reverse legend point to it. However, the
weight is light since it isn't gold all the way through (would be in the low 4g range if it was). Solidi from
Carthage at this time were low in
diameter but thick to make up for it (globular).
I can't see or make out any possible characters to the left or right of
Heraclius or
Tiberius nor can I make out anything below the base. So, the best I can do is
Sear 1188 (DO 43),
Sear 1189 (DO 44-7) or
Sear 1189A (DO —). The date range for all these would be from ca. AD 675 to 682. The rest of the details are:
Obverse:
(or similar - I can't make anything out on your coin)
Bust facing (or three-quarter
face to right), with short beard, wearing helmet and
cuirass, and holding spear and
shield.
Reverse: No
legendCross potent on three steps between facing standing figures of
Heraclius (on left) and
Tiberius (on right), each wearing crown and
chlamys, and holding
globus cruciger.
Various characters to right and/or left and/or at base that can't be made out on your coin.
As for who made it, I can only personally speculate that it was from Arabs who were nearby and who would conquer the city in the following decade (AD 698). I
hope someone more knowledgeable sees this though and can share the actual answer.
Kevin