Yes, that is an engraver's error: he left out the O of CONSTAN - TIVS.
Such errors do occur on official coins, though not very often. For example, in an earlier era, GABA for
GALBA on middle bronzes of
Galba (
BMC 149), and
GEM for
GERM on
asses of
Domitian (
RIC 489 note).
Such errors are of no historical importance, though they are numismatically interesting for showing official mistakes, and because of their
rarity. Usually they only occur on one die within the issue in question.
Your error does not appear to be published. It was unknown both to
Kent in
RIC VIII, Trier 122, and to Deyperot in Les monnaies d'or II, Treves 4/3. Both
Kent and
Depeyrot report that there were 45 specimens of this
solidus in the
Portugal hoard, and
Depeyrot had studied 44 other examples, apart from those reported to be in the
hoard. But neither of these authors
had seen a specimen with the O omitted from Constantius' name, unless of course they looked too quickly, and failed to notice the missing O on a specimen that they
had indeed seen!
Please show us the
reverse of your coin too!
