Eros was a powerful force in ancient Greece, but it expressed itself mainly in homosexuality. The practice was common in Athens, but the Spartans were especially notorious for it, encouraging it in their gymnasiums and using homosexual attachments to build solidarity among soldiers in war. Historian Michael Grant writes that Eros was also the basis for the practice of pederasty. He notes that sexual relations between men and boys were “far more favored than homosexual relations between men of the same age.” The ancients also erected an educational philosophy based on pederasty. As historian K. J. Dover describes it, the man always played the active role and the boy the passive role. The whole project was conceived of in terms of an exchange; the young boy agreed to sexualrelations with an older man and in return he received knowledge and tutoring.