Watch List notes:

MACEDON. Beroea, Metropolis of the Koinon of Macedon. Period of Gordian III, 238-244. Triassarion (Bronze, 28 mm, 13.74 g, 1 h). AΛEZANΔPOY Head of Alexander in lion's skin headdress to right, below, star. Rev. ΚΟΙ ΜΑΚΕΔΟΝΩΝ B NEΩ BEPOIE Olympias seated left, feeding a serpent rising from a cista mystica before her. AMNG 861. Extremely rare, and a particularly interesting type. Some roughness and corrosion, especially on the reverse, otherwise, nearly very fine.
From a European collection formed before 2010.

It might be worth trying to professionally clean this reverse!.