Ahh, it is all clear now thanks to your post Ross.
The tag identified this coin as
Justinian II. I did not notice but similar square
types are also attributed to other emperors. I now have this...
References attribute these squared
types to the Senate of the City of
Rome during the final stage of
Byzantine rule, c. 690 - 720 (and perhaps a little later).
Portraits vary and are identified as various emperors reigning during this period.
Grierson identifies the
portrait on this coin as the young
Constantine V, at the beginning of
his joint rule with
his father
Leo III, c. 720 A.D.
Grierson has commented, in view of the specimens in the Byzantine-Papal
hoard, the low
weight combined with a relatively high value suggests that these squared 30 nummi
types may have been intended as a
billon rather than copper coinage.
Murari confirmed traces of silver exist on many of the three-quarter folles he handled.