The coin is Roman. It's a coin of Constantius II, a Half-Centenionalis
Obverse: D N CONSTANTIVS P F AVG, diademed, draped & cuirassed bust right
Reverse: FEL TEMP REPARATIO, Soldier advancing left, spearing a fallen horseman, gamma to left.
It's not worth much in the shape it's in, but still an authentic ancient and a nice find.
Do you live in the Europe or the UK ? If so there may be others in the same location.
Roman soilders often burried their money before heading to battle.
Regards
Allen