Historical background
This summary, revised in June 2003, updates the more extensive treatment of the identification of the city at Kerkenes with Pteria (Summers, 1997) a capital of the Medes, mentioned by Herodotus whose testimony is worth quoting in full:
Croesus, when he had crossed [the Halys river] with his army, came in Cappadocian territory, to what is called Pteria. Pteria is the strongest part of all that country and lies in a line with the city of Sinope, on the Euxine Sea. There he encamped, destroying the farms of the Syrians and he captured the city of the Pterians and made slaves of the people, and he captured all the neighbouring towns; moreover he drove the Syrians from their homes, though they had done him no manner of harm. Cyrus, on his side, gathered his own army, and took on, as well, all the peoples who lived between him and Croesus. (Before he set out to march at all, he sent heralds to the Ionians and tried to make them desert Croesus. But the Ionians would not listen to him). So when Cyrus came and encamped over against Croesus, then and there in that land of Pteria they fought against one another with might and main. The battle was fierce, and many fell on both sides. At last they broke off at the onset of night, without either having the victory; so hard did the two armies fight.
The historical background to the Battle of Pteria begins with the Median attack on the Neo-Assyrian city of Nimrud in 614 BC, their subsequent alliance with the Babylonians and sack of Nineveh to the combined forces two years later. Sources for the following period of Median expansion are few and much debated, being Greek and Babylonian rather than Median and mostly somewhat later than events themselves. By 590-589 BC the Medes were fighting the Lydians in Central Anatolia. The power of Urartu must have been spent because the Median king Cyaxares could not have campaigned towards the Halys River without security in the rear. The Medio-Lydian war, a series of annual campaigns lasted into a sixth year when on the afternoon of 28 May 585 BC, it seemingly came to an end with the Battle of the Eclipse.
War subsequently broke out between the two countries and lasted for five years, during which both Lydians and Medes won a number of victories. One battle was fought at night. But then, after five years of indecisive warfare, a battle took place in which the armies had already engaged when day suddenly turned into night. This change from daylight into darkness had been foretold to the Ionians by Thales of Miletus, who fixed the date for it for the year in which it did, in fact, take place. Both the Lydians and the Medes broke off the engagement when they saw this darkening of the day: they were more anxious than they had been to conclude peace, and a reconciliation was brought about by Syennesis of Cilicia and Labynetus of Babylon, who were the men responsible both for the pact to keep the peace and for the exchange of marriages between the two kingdoms. They persuaded Alyattes to give his daughter Aryenis to Astyages, son of Cyaxares - knowing that treaties seldom remain intact without powerful sanctions.
The next part of the story begins with the overthrow of Astyages and the establishment of the Achaemenid Empire by Cyrus the Great. By this time Alyattes was dead and his son Croesus, brother-in-law of Astyages, was on the Lydian throne. Turmoil in the Iranian court provided Croesus with an opportunity. Using the convenient, if not genuine, excuse of the murder of his brother-in-law, and having sent envoys to various oracular temples from which he received what he could only interpret as a favorable answer he took his forces across the Halys River and sacked Pteria, as recounted in the passage from Herodotus quoted above. After the inconclusive Battle of Pteria between Croesus and Cyrus, Croesus retreated to Sardis for the winter from where he summoned his allies in the natural expectation that Cyrus too would withdraw for the winter and that the confrontation would be renewed in the following spring. Cyrus, however, went in immediate pursuit. The oracle at Delphi had been correct. An empire was destroyed as a consequence of Croesus's action but not, as he had so confidently expected, that of the Persians but rather his own.
The brief period of occupation at Kerkenes fits with the historical record: perhaps founded as the capital of an Anatolian polity towards the middle of the seventh century BC, falling under the control of the Medes by 585 BC and destroyed by Croesus some forty years later. The site would be consistent with the need of Astyages for a strong base east of the Halys River, and the lack of later occupation can easily be understood because once Cyrus had exerted control over Lydia, the very reason for a strong base east of the Halys River no longer existed.
It is striking that Croesus treated the inhabitants of Pteria differently from the "Syrians" in the surrounding villages who, in contrast to the Pterians, had done no wrong. It can thus be argued that the phraseology of Herodotus implies that the inhabitants of Pteria were not the same as the rural population, an implication that can easily be understood if the occupants of the city were Medes and their allies: a foreign occupying power.
A much later author, Stephanos of Byzantium, as Przeworski noted, lists both Pteria near Sinop, and Pterion (alternatively Pteria), a city of the Medes. David French has suggested (pers. comm.) that the association of the name Pterion/Pteria with the Medes supports the identification of the Median city on the Kerkenes Dag with Herodotus' Pteria.