Having thus secured the city from all danger of an immediate attack, Themistocles pursued his favourite project of rendering Athens the greatest maritime and commercial power of Greece. He erected a town round the harbour of Piraeus, distant between four and five miles from Athens, and enclosed it with a wall as large in extent as the city itself, but of vastly greater height and thickness. Meanwhile an event occurred which secured more firmly than ever the maritime supremacy of Athens, by transferring to her the command of the allied fleet. In the year after the battle of Plataea a fleet had been fitted out and placed under the command of the Spartan regent, Pausanias, in order to carry on the war against the Persians. After delivering most of the Grecian towns in Cyprus from the Persians, this armament sailed up the Bosporus and laid siege to Byzantium, which was garrisoned by a large Persian force. The town surrendered after a protracted siege; but it was during this expedition that the conduct of the Spartan commander struck a fatal blow at the interests of his country. The immense booty, as well as the renown, which Pausanias had acquired at Plataea, had filled him with pride and ambition. After the capture of Byzantium he despatched a letter to Xerxes, offering to marry the king's daughter, and to bring Sparta and the rest of Greece under his dominion. Xerxes was highly delighted with this letter, and sent a reply in which he urged Pausanias to pursue his project night and day, and promised to supply him with all the money and troops that might be needful for its execution. But the childish vanity of Pausanias betrayed his plot before it was ripe for execution. Elated by the confidence of Xerxes, and by the money with which he was lavishly supplied, he acted as if he had already married the Great King's daughter. He assumed the Persian dress; he made a progress through Thrace, attended by Persian and Egyptian guards; and copied, in the luxury of his table and the dissoluteness of his manners, the example of his adopted country. Above all, he offended the allies by his haughty reserve and imperiousness. His designs were now too manifest to escape attention. His proceedings reached the ears of the Spartans, who sent out Dorcis to supersede him. Disgusted by the insolence of Pausanias, the Ionians serving in the combined Grecian fleet addressed themselves to Aristides, whose manners formed a striking contrast to those of the Spartan leader, and begged him to assume the command. This request was made precisely at the time when Pausanias was recalled; and accordingly, when Dorcis arrived, he found Aristides in command of the combined fleet (B.C. 478).