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This is an ancient Iron Age Celtic billion silver stater of the British Durotriges Tribe. It was minted between the mid 1st century BC to the mid 1st century AD with the invasion of the Romans.
Obverse: Devolved head of Apollo right
Reverse: Disjointed horse left; pellets above, pellet below, pellet in lozenge above tail, [zigzag and pellet pattern between two parallel exergue lines].
MATERIAL: Billion (base silver)
DATE: 58 BC - 45 AD
SIZE: 17mm dia
WEIGHT: 1.92 grams
ATTRIBUTION: ABC 2166; V.1235, 52, 54, 55, BMC 2525-2731. Spink 367.
PROVENANCE: Private collection. Bristol, United Kingdom.