Actually, um, The Bible did sort of exist prior to Sparta; it's been around for thousands of years...Wait...you used "bible" (non-specific book); Sparta did exist before books, so yeah, you're right! (sorry; flip answer...)
Why does everyone assume that? The bible is just The Torah with another section slapped on called the New Testament. The bible may not have existed but the Torah did which is just the Old Testament for Christians. And in Christ's day, it wouldn't have been a book, The Bible would've been a huge scroll. Second, the Torah already downcast the idea of being gay.
According to Genesis God made man and woman, not man and man. If man were meant by nature to marry another man, then the human race would've ended when Adam #1 and Adam #2 died.
I'm not against gay marriage nor am I for it. What I believe, is gay marriage is fine, as long as there are those who would remain straight and actually make the babies that gays cannot makje and have to adopt.