From Frequently Asked Questions About the Bible and Homosexuality:
The ancients, as MIT's David Halperin notes: "conceived of 'sexuality' in non-sexual terms: What was fundamental to their experience of sex was not anything we would regard as essentially sexual. Rather, [sex] was something essentially social -- namely the modality of power relations that informed and structured the sexual act." In the ancient world, sex was "not intrinsically relational or collaborative in character; it is, further, a deeply polarizing experience: It serves to divide, to classify, and to distribute its participants into distinct and radically dissimilar categories. Sex possesses this valence, apparently because it is conceived to center essentially on, and to define itself around, an asymmetrical gesture, that of the penetration of the body of one person by the body, and, specifically, by the phallus -- of another ... The proper targets of [a citizen's] sexual desire include, specifically, women, boys, foreigners, and slaves -- all of them persons who do not enjoy the same legal and political rights and privileges that he does." Today's society values and practices sexuality in entirely different terms: love, relationship, mutual respect.(Editorial notes in square brackets above appear on the web page from which this is copied.)
(Hmm ... the implication that modern practice matches modern values sounds simplistic and idealistic ...)