THRACE, Byzantion
AE25. 10.44g, 25mm
MINTED: THRACE, Byzantion, in alliance with BITHYNIA, Kalchedon, circa 3rd-2nd centuries BC.
REF: SNG BM Black Sea 83; CNT online 3604-5
OBVERSE: Veiled head of Demeter right.
REVERSE: BYZAN / KAΛXA, Poseidon seated right on rocks, holding aplustre and trident; monogram to inner right.

Notes:
Weathered forest-green patina.
An interesting issue, the reverse naming both Byzantion and Kalchedon, evidence of an alliance between the two cities that stood on opposite shores of the straits of Bosporus.
 
Historical Notes:
Byzantion (Byzantium in Latin) was founded in the 7th century BC by colonists from the Greek city of Megara.  Situated on the European shore of the Bosporus, its large protected natural harbour and advantageous location allowed it to control the passage between the Black Sea and the Sea of Marmara.  Over the course of its history, the strategic importance of Byzantion would see it fought over by the Persians and the Greeks, and then Athens and Sparta.  It was conquered by Alexander the Great in the course of his campaign against Darius III, and in the aftermath of Alexander's death and the great wars between his successors, was the site of the Battle of Byzantium in 317 BC between Antigonus I Monopthalmus and Cleitus the White. 
 
During the Roman period, Byzantion would continue to flourish, and in AD 330, Emperor Constantine I, appreciating its many virtues, refounded it as Constantinople (the city of Constantine), and made it the new capital of the empire.  As the crossing point between Europe and Asia, the city would arguably grow even more important after the fall of the Roman Empire, becoming the capital of the Byzantine Empire, until its eventual conquest by the Ottoman Turks in 1453.  It is today known as Istanbul, the capital of Turkey.