MOESIA, Istrus, AE23 Pan-, magistrate 3rd century B.C. Obv: Veiled and wreathed head of Demeter, right. Countermark: helmeted head of Athena, right. Rev: IΣTPIH above sea-eagle on dolphin, left; grain ear in left field. [ΠA]N below. Cf. SNG Stancomb 199 HGC 3.2 1818 21 mm, 4.94g ex William Stancomb Collection Is there somewhere I can learn more about the countermark? I can find information about countermarks on Roman coins, but I don't know of any sites that discuss Greek countermarks. Idea idea who might have added this one?