Not to mention John Boswell's books

A recent article in the Journal of Modern History, "Same-Sex Couples Creating Households in Old Regime France: The Uses of the Affrèrement", seems to suggest that there may be a historical precedent for same-sex civil unions, dating back 600 years in France. I haven't read the article yet, but here's an article about it:

[I]n late medieval France, the term affrèrement -- roughly translated as brotherment -- was used to refer to a certain type of legal contract, which also existed elsewhere in Mediterranean Europe. These documents provided the foundation for non-nuclear households of many types and shared many characteristics with marriage contracts, as legal writers at the time were well aware, according to Tulchin.

The new "brothers" pledged to live together sharing 'un pain, un vin, et une bourse' -- one bread, one wine, and one purse. As Tulchin notes, "The model for these household arrangements is that of two or more brothers who have inherited the family home on an equal basis from their parents and who will continue to live together, just as they did when they were children." But at the same time, "the affrèrement was not only for brothers," since many other people, including relatives and non-relatives, used it.

The effects of entering into an affrèrement were profound. As Tulchin explains: "All of their goods usually became the joint property of both parties, and each commonly became the other's legal heir. They also frequently testified that they entered into the contract because of their affection for one another. As with all contracts, affrèrements had to be sworn before a notary and required witnesses, commonly the friends of the affrèrés."

Tulchin argues that in cases where the affrèrés were single unrelated men, these contracts provide "considerable evidence that the affr`rés were using affrèrements to formalize same-sex loving relationships. . . . I suspect that some of these relationships were sexual, while others may not have been. It is impossible to prove either way and probably also somewhat irrelevant to understanding their way of thinking. They loved each other, and the community accepted that. What followed did not produce any documents."