During the war between the gods and giants, Mars was so eager to prove his skill in warfare that he engaged in a fierce battle with Otus and Ephialtes. These two giants were only nine years old; but they were already of immense size, as they increased in height at the rate of nine inches every month. The young giants were very proud of having conquered the god of war, and carried him off the battle-field in triumph. They bound Mars with iron chains, and kept a careful guard over him so that none of the gods could set him free. Whenever Mars attempted to escape at night, believing that the giants were asleep, the rattle of the chains woke his guardians, and all hope of rescuing him was over. In this disgraceful bondage the unhappy Mars lingered for fifteen months until Mercury, the prince of thieves, unfastened the chains and restored the god to freedom. When Cadmus went on his search for his sister Europa, whom Jupiter, in the form of a white bull, had carried off to a distant land,[33] the devoted brother was at last bidden to give up his hopeless quest, to settle in the country, later called Bœotia, and to found a city there. Cadmus was glad to rest after his long march, and he sent some of his men in search of a spring. When they did not come back, he sent others to look for them, and when these did not return, he went himself to see what had caused all this delay. He carried his sword in his hand, and also a long spear, for he guessed that some disaster had overtaken his men. He wandered some time before he discovered any trace of them, and then at the edge of a forest he came upon the lifeless body of one of those who had first set out to find the spring. As he went farther into the forest he found others of his men, all of them lifeless, and soon he came to a large cave, at the entrance of which bubbled a fountain of purest water.