Jamieson, Fausset and Brown on Ezra 6:2

2. Achmetha--long supposed to be the capital of Greater Media (the Ecbatana of classical, the Hamadan of modern times), [is] at the foot of the Elwund range of hills, where, for its coolness and salubrity, Cyrus and his successors on the Persian throne established their summer residence. There was another city, however, of this name, the Ecbatana of Atropatene, and the most ancient capital of northern Media, and recently identified by Colonel Rawlinson in the remarkable ruins of Takht-i-Soleiman. Yet as everything tends to show the attachment of Cyrus to his native city, the Atropatenian Ecbatana, rather than to the stronger capital of Greater Media, Colonel Rawlinson is inclined to think that he deposited there, in his fortress, the famous decree relating to the Jews, along with the other records and treasures of his empire [Nineveh and Persepolis].