This coin is listed in RIC, but there is no workshop listed, because it was unclear. Several examples of this coin have surfaced over the years. This example has the captive looking straight ahead, which is mentioned on the footnotes.
Constantine I
A.D. 316- 317
19x20mm 2.6gm
IMP CONSTANTINVS P F AVG; laureate, draped and cuirassed bust right, seen from rear.
SOLI INVICTO COMITI; Sol rad., stg. L., raising r. hand, globe in l., chlamys across l. shoulder, captive to left wearing Phrygian cap looking straight ahead.
in ex. RT
RIC VII Rome 51