Gold aureus, 19mm, 6.95gm, issued AD 66/67 Rome mint.
Obv: IMP NERO CAESAR AVGVSTVS, Laureate head right.
Rev: IVPPITER CVSTOS, Jupiter, cloak round lower limbs, seated left on throne, holding thunderbolt and long sceptre.
References: see Sear 1930, RIC 63.
Custos was the facet of Jupiter as a Guardian of the Emperor. This type was issued in thanks after the failure of the Piso conspiracy in AD 65 (see Tac. Ann. 15.48-74). Tacitus reports that a weapon that was to be used against Nero was dedicated by the Emperor in a temple and inscribed to Jupiter.
This coin fits the following collection focus(es): Twelve Caesars.