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This is an ancient Roman silver Siliqua of emperor Valentinian, dating to 367 - 375 A.D.
D N VALENTINIANVS P F AVG Pearl diademed, draped & cuirassed bust right
VRBS-ROMA, Roma seated left on throne, holding Victory on globe and scepter
This coin was minted at Trier in Germany, mintmark TRPS dot. It had travelled across the English Channel, being discovered by a metal detectorist in Yorkshire. It has a striking crack and a wavy flan but is solid and stable.
DATE: 367-375 A.D.
MINTMARK: TRPS (Trier, Germany)
SIZE: 17.54mm dia
WEIGHT: 1.78 grams
ATTRIBUTION: RIC IX Trier 27d.