COIN (ROMAN)
Denarius of the Roman Republic, struck by the moneyer Cn Domitius, Rome, dating to 116 or 115 BC. It is 19mm in diameter and weighs 3.38g. 

Republican coins such as these are quite likely to have come into the country with the legions at the time of the conquest. 

Ref: Roman Republican Coinage 285/1.
Ruler: Republic
Moneyer: Domitius Ahenobarbus, Cn.
Denomination: Denarius (Roman Republic)
Material: Copper alloy
Mint: Rome
Obverse: Helmeted head of Roma, right; behind, denominational mark. Border of dots.
Obverse legend: ROMA X
Reverse: Jupiter in quadriga, right, holding thunderbolt in left hand and branch in right hand. Line border.
Reverse legend: CN·DOMI
Dated: -116.0 to -115.0
Weight (g): 3.38
Diameter (mm): 19.0
Parish: Chiseldon
District: Swindon
County: Swindon
Region: South West
Discovery method: Metal detector
RRC reference: rrc-285.1