Mygdonia (; ) was an ancient territory, part of Ancient
Thrace, later conquered by
Macedon, which comprised the plains around
Therma (
Thessalonica) together with the valleys of Klisali and Besikia, including the area of the
Axios river mouth and extending as far east as Lake
Bolbe. To the north it was joined by
Crestonia. The
Echeidorus, which flowed into the
Thermaic Gulf near the marshes of the Axios, had its sources in Crestonia. The pass of Aulon or
Arethusa was probably the boundary of Mygdonia towards
Bisaltia. The maritime part of Mygdonia formed a district called
Amphaxitis, a distinction which first occurs in
Polybius, who divides all the great plain at the head of the Thermaic gulf into Amphaxitis and
Bottiaea, and which is found three centuries later in
Ptolemy. The latter introduces Amphaxitis twice under the subdivisions of Macedonia---in one instance placing the mouths of the Echidorus and Axios in Amphaxitis, and mentioning Thessalonica as the only town in the district, which agrees with Polybius and with
Strabo. In another place Ptolemy includes
Stageira and Arethusa in Amphaxitis, which, if correct, would indicate that a portion of Amphaxitis, very distant from the Axios, was separated from the remainder by a part of Mygdonia; but since this is improbable, the word is perhaps an error of the text.