The Marriage of Likeness by John Boswell
In this work, John Boswell attempts to prove that in pagan antiquity and during Christianity's first centuries - for around 2000 years in all - extensive legal sanction was given to pairing between males. He also shows that society had little difficulty in accepting homosexual relationships. The book claims that Christendom has had a major homosexual past which religious authorities have spent hundreds of years vigorously attempting to suppress and ignore.