Well preserved ancient coin!
This Gold coin is from the joint reign of the Emperors Constans II and Constantine IV (A.D. 654 to 668). Constans II (who was also known as Constantine the Bearded) was Byzantine Emperor from 641 to 668. He was also the last emperor to become consul in 642, which made him the last Roman consul in history. Constans II reigned jointly with his son Constantine IV from 654 to 668. This coin was issued during that time. The obverse shows a fully bearded Constans at left, with Constantine next to him. The reverse features a cross potent atop three steps. Two phrases are also shown on the reverse: "CONOB" which is a abbreviation of the Greek for "Byzantine coinage," and "VICTORIA AVGY."
This Gold coin weighs approx. 4.3 grams. This example is nicely centered and certified Mint State by NGC. It is rated 5/5 strike; 4/5 surface.