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This is an ancient Roman gold Solidus of emperor Valentinian III dating to 425 - 455 AD.
D N PLA VALENTI IANVS P F AVG diademed, draped and cuirassed bust right
VICTORI A AVGGG emperor standing facing, foot on facing, human-headed serpent (with closed coil)
This coin was struck at the Ravenna mint in Italy.
This coin is ex mount/jewellery and has marks on the back
DATE: 327 - 330 A.D.
MINTMARK: COMOB R.V. (Ravenna, Italy)
SIZE: 22mm dia
WEIGHT: 4.42 grams
ATTRIBUTION: RIC 2011, Cohen 19.