Por el tamaño y el peso de esto podría ser Semisse de Nerón
Nero, 13 October 54 - 9 June 68 A.D.
http://dl.dropbox.com/u/11761319/Semisse%20Nero.jpg
Orichalcum as, RIC I 219, VF, Rome mint, 7.819g, 25.1mm, 180°, c. 64 A.D.; obverse NERO CLAVDIVS CAESAR AVG GER P M TR P IMP P P, laureate head right; reverse GENIO AVGVSTI S C, Genius standing left, holding patera and cornucopia, altar at left, I in ex; attractive green patina, nice style, high relief portrait; rare (R2