Yes, Ebbie, a certain number of same-sex unions were found in most ancient societies (and maybe all of them). For sure. But they weren't called "marriages", and I think that's mainly because they couldn't produce children. A relationship that brings forth children is naturally about the most important thing going on in any society...because it secures the future of the nation and the stability of civil society. Other love relationships are desirable too, but they are not so vital to the future of the community, therefore they are given less importance and less ceremonial emphasis...if any. They become, in effect, informal private relationships which are a matter of private choice by those involved.

That would also apply to what the Indians called "teepee-creeping" or we might call "playing the field". ;-)

I'm not sure when the "modern" form of marriage as we know it began, but I would think it was a very long time ago, so maybe it's not modern at all.