The military talents of Alexander were untried, and of course unknown; the perils which he had to encounter were patent.

Codomannus may be excused if for some months after Alexander's accession he slackened his preparations for defence, uncertain whether the new monarch would maintain himself, whether he would overpower the combinations which were formed against him in Greece, whether he would inherit his father's genius for war, or adopt his ambitious projects.

It would have been wiser, no doubt, as the event proved, to have joined heart and soul with Alexander's European enemies, and to have carried the war at once to the other side of the Egean.

But no great blame attaches to the Persian monarch for his brief inaction.
As soon as the Macedonian prince had shown by his campaigns in Thrace, Illyria, and Boeotia that he was a person to be dreaded, Darius Codomannus renewed the preparations which he had discontinued, and pushed them forward with all the speed that was possible.

A fleet was rapidly got ready: the satraps of Asia Minor were reinforced with troops of good quality from the interior of the Empire, and were ordered to raise a strong force of mercenaries; money was sent into Greece to the Lacedaemonians and others in order to induce them to create disturbances in Europe; above all, Memnon the Rhodian, a brother of Mentor, and a commander of approved skill, was sent to the Hellespont, at the head of a body of Greeks in Persian pay, with an authority co-ordinate to that of the satraps.
A certain amount of success at first attended these measures.