When Pausanias succeeded in taking Byzantium, which we now know as Constantinople, his pride and ambition increased, and he determined to play into the hands of the Persian king. So he sent for some of the prisoners, and, setting them free, he bade them carry letters to Xerxes their king. In these letters he offered, as only a traitor could do, to subdue Sparta and the other states of Greece, and to hold them for the Persian monarch. He asked Xerxes to grant him money to carry on the war, and as a reward for his services he requested the hand of his daughter. Pausanias hoped in this way to gain his great ambition and become tyrant of all Greece. Xerxes was pleased with the Spartan’s letter, nor did he stay to wonder if so disloyal a citizen would be a faithful ally. He sent a letter to bid the traitor ‘work on night and day to accomplish his purpose, without letting himself be held back by lack of gold or silver, or want of troops, for all should be at his command.’ When Pausanias held the king’s letter in his hand, and saw the king’s money at his disposal, he began to behave as though he was already the son-in-law of the great king. He clad himself as a Persian prince, he journeyed from place to place in royal state, attended by Persian guards. The Spartan simplicity in which he had been trained was forgotten, and he lived in as great luxury as did his new friends. Rumours of the strange way in which Pausanias was behaving soon reached Sparta. When it was found that the rumours were true, Pausanias was ordered to come home, and another commander, named Dorcis, was sent to take his place. But before Dorcis reached Byzantium, the fleet had refused to obey Pausanias and had placed itself under Aristides, the admiral of the Athenian ships. A league, called the Delian League, was then formed, to enable Greece to carry on the war against Persia. It was named the Delian League because its treasures were kept in the temple of Apollo, on the sacred island of Delos. Athens became the head of the league, Aristides its leader, and so greatly was he trusted that he was asked to arrange the sum of money or the number of ships which each city belonging to the league should provide. Most of the Greek cities in the Ægean islands joined the Delian League, as well as those on the north and east coasts of the Ægean Sea. Those who joined took solemn oaths to be true to the demands of the league, and their oaths were ratified by sinking masses of iron in the sea. Not until these reappeared might the people be set free from the vows which they had taken. Pausanias had now returned to Sparta, where he was thrown into prison. But though there was abundant proof of his foolish conduct there was none of his treachery, and he was soon set free. The traitor continued to send letters to Xerxes by his slaves, and those who carried them never returned, for Pausanias feared lest they should betray him.