I have researched this Tetradachm, unsuccessfully. I was thinking this might represent a Greek City State that was known for its horses; I could not find anything showing just the horses head. Help, please.
How much does your tet weigh? Possibly Alexander III. 336-323 BC. AR Corinth mint. Struck under Demetrios Poliorketes, circa 310-290 BC. Head of Herakles right wearing lion's skin headdress / BAΣIΛEΩΣ AΛEΞANΔΡOΥ, Zeus seated left, holding eagle and sceptre; horse head left in left field. Price 689; Müller
..its some kind of control mark....i would go with @Ryro on who's name its minted in....it is a neat coin!
Corinthian coins had Pegasus on their reverses. I suppose numismatists attributed these tets to the Corinth mint because of this horse head, interpreted as the head of Pegasus.
It's a bit difficult to tell from the photo, but the legs don't appear crossed, nor do I see ΒΑΣΙΛΕΩΣ . Therefore, I'm thinking it may be Price 59, which would place it from Amphipolis.