Istros was an ancient city near the mouth of the Danube River, in today's Romania. Its coins have an intriguing obverse, as they depict two juvenile heads facing in opposite directions.
The image could allude to the rising and the setting of the sun god Helios. Another possibility is that it relates to a geographical myth current in Antiquity of the two branches of the Danube River. It was known that one of the branches empties itself into the Black Sea; while the other was supposed to end in the Adriatic Sea. The Danube thus, people believed, connected the two important trade routes to the east and to the west.
The reverse of our half obol depicts a sea eagle catching a dolphin. This motif was adopted from the early bronze coins of Olbia.