Neilin G., Rehm E. (eds.) Achaemenid Impact in the Black Sea. Communication of Powers

Aarhus, Denmark: Aarhus University Press, 2010. — 325 p.A short historical overview.
For 200 years, from the second half of the sixth century to the decades before 330 BC, the Persian dynasty of the Achaemenids ruled Anatolia and Armenia as part of an enormous empire stretching from the Mediterranean Sea to Afghanistan and India. The Great Kings Dareios I and Xerxes I even tried to conquer Greece and the northern Black Sea territories. Although they failed, parts of Thrace did become part of their dominion for a short period. The Pontic Greeks were able to take advantage of the situation by aligning themselves with Persian supremacy, which might have been a tempting alternative to joining the Athenian-led Delian League.
As the Great Kings in Persepolis lost interest in their northwestern border, their satraps had to handle the situation, maintaining the balance of power by entering into various alliances with Greek and probably also Scythian factions. This was a stable solution and the satraps became so adept at playing this ‘Anatolian plan’ that a desire for independence arose.
From 400 BC onwards, with the rebellion of Cyrus the Younger, as documented by Xenophon, a series of internal struggles started to weaken parts of the Empire. This situation was beneficial to the peripheries, for example, the Bosporan Kingdom, and led to a new level of acculturation at the expense of the Persians in the first half of the fourth century. In a kind of globalization effect, the established Greek polis communities were also destabilized during the same period, so that, finally, nobody could resist the new rising power of the Macedonians.
In contrast to some of the other satrapies, such as Egypt, Phoenicia and Syria, the Black Sea had no prosperous cities or provinces to offer.
The question always rises as to why the Great Kings were interested in the western and northern Pontic zones. One possible answer might be the desire to conquer every part of the known world. After 479 BC, it seems that the Great Kings acknowledged the fact that the coast and the Caucasus formed the natural borders of their Empire. The satraps, on the other hand, could not avoid becoming involved in the affairs of the Black Sea region in order to safeguard the frontiers they had established. They had to incorporate the Greeks, as accepted inhabitants of their province, into the Persian administrative system. Possibly they achieved this by granting them the monopoly in sea trade and using the Anatolian Greeks as the main active bearers and transmitters of Persian customs and culture. More research into this chapter of Persian history is still required.