This silver obol was minted around 500 BC in the Greek city of Miletus in Asia Minor. At that time Asia Minor, and with it Miletus, were part of the vast Persian Empire under Great King Darius I, who around the turn from the 6th to the 5th century was just busy introducing the first Persian silver and gold coins, and therewith creating an official imperial currency for the first time.
From a modern point of view one might expect that the local mints within the empire stopped issuing their own coins now, and adopted the imperial coinage. Yet in the Persian Empire, this was not the case. Local issues were not seen as competitions for the imperial currency, but as an important addition and as a basis for trade. Hence Miletus continued to strike coins with the head of the lion, the emblem of the city.