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This is an ancient Roman silver Miliarense of emperor Valens, dating to 364 - 367 A.D.
DN VALEN-S PF AVG, pearl-diademed, cuirassed bust right
VICTORIA AVGVSTORVM, Victory standing right, left foot on globe, inscribing VOT V MVLT X on shield resting on cippus
This coin was minted in Rome, mintmark RB. It had traveled across the empire, being buried in the Thruxton Hoard in England. This coin was purchased directly from the finder after being disclaimed by the British Museum.
DATE: 364 - 367 A.D.
MINTMARK: RB (Rome)
SIZE: 22mm dia
WEIGHT: 4.1 grams
ATTRIBUTION: RIC IX 8b corr., B. RIC IX Rome 8b corr. (bust type); RSC 60.