Marriage laws that cover both heterosexual and homosexual couples go back only about three years. Such laws exist in the Netherlands, Belgium and two provinces in Canada. Gay civil unions exist in Denmark, Norway and several other European nations. In the U.S., attempts by gays to get a marriage license date back at least to the early 1970s. But some historians have found references to gay marriage dating back to classical times. NPR's Margot Adler reports.