Before this time, probably, the whole Asiatic coast northward of Miletus—including the Ionic and Æolic cities and the principality of Memnon—had either accepted willingly the dominion of Alexander, or had been reduced by his detachments. Accordingly he now directed his march southward from Miletus, towards Karia, and especially towards Halikarnassus, the principal city of that territory. On entering Karia, he was met by Ada, a member of the Karian princely family, who tendered to him her town of Alinda and her other possessions, adopting him as her son, and entreating his protection. Not many years earlier, under Mausôlus and Artemisia, the powerful princes of this family had been formidable to all the Grecian islands. It was the custom of Karia that brothers and sisters of the reigning family intermarried with each other: Mausôlus and his wife Artemisia were succeeded by Idrieus and his wife Ada, all four being brothers and sisters, sons and daughters of Hekatomnus. On the death of Idrieus, his widow Ada, was expelled from Halikarnassus and other parts of Karia by her surviving brother Pixodarus; though she still preserved some strong towns, which proved a welcome addition to the conquests of Alexander. Pixodarus, on the contrary, who had given his daughter in marriage to a leading Persian named Orontobates, warmly espoused the Persian cause, and made Halikarnassus a capital point of resistance against the invader.[218] [218] Arrian, i. 23, 11, 12; Diodor. xvii. 24; Strabo, xiv. p. 657. But it was not by him alone that this city was defended. The Persian fleet had repaired thither from Miletus; Memnon, now invested by Darius with supreme command on the Asiatic coast and the Ægean, was there in person. There was not only Orontobates with many other Asiatics, but also a large garrison of mercenary Greeks, commanded by Ephialtes, a brave Athenian exile. The city, strong both by nature and by art, with a surrounding ditch forty-five feet broad and twenty-two feet deep,[219] had been still farther strengthened under the prolonged superintendence of Memnon;[220] lastly, there were two citadels, a fortified harbor, with its entrance fronting the south, abundant magazines of arms, and good provision of defensive engines. The siege of Halikarnassus was the most arduous enterprise which Alexander had yet undertaken. Instead of attacking it by land and sea at once, as at Miletus, he could make his approaches only from the land, while the defenders were powerfully aided from seaward by the Persian ships with their numerous crews. [219] Arrian, i. 20, 13. [220] Arrian, i. 20, 5. ξύμπαντα ταῦτα Μέμνων τε αὐτὸς παρὼν ἐκ πολλοῦ παρεσκευάκει, etc.