The Great Debate about whether people of the same sex should be allowed to ‘marry’ would have bewildered the Romans, and not because they had any hang-ups about that style of sexual behaviour either.
For legal purposes, Romans defined the familia (‘household’) as Roman citizens, joined in lawful marriage, producing legitimate children and with some property to transmit by inheritance. But as the Latin matrimonium (our ‘matrimony’) makes clear, the main point about marriage is that it is all about the mater, ‘mother’. The family gives its daughter into matrimonium, the husband leads, receives and keeps his wife in matrimonio. The Latin for ‘wife’, uxor (cf. our ‘uxorious’), seems to be etymologically related to a Sanskrit word meaning ‘sprinkle with seed’.
‘[Marriage] was ordained for the procreation of children’, says the Anglican Prayer Book, and a Roman would have agreed: ‘the state cannot survive without numerous marriages’, says Aulus Gellius. The production of legitimate citizen children was the basic purpose. This was the only way to continue the family blood-line, its traditions, its worship, its privileges and (as Romans stress) its support for the old. Romans were well aware of these wider advantages. As the first century ad Stoic Musonius writes, there must be ‘perfect companionship and mutual love... both in health and sickness and under all conditions, since it was with desire for this as well as having children that both entered upon marriage’.
We live in a world where marriage is no longer seen as essential for the production of children. Legitimacy is not the serious matter it was in the ancient world. Citizenship, again, is a matter of residence almost as much as of blood-line. The main question, then, is how far we need any more the term ‘marry’ to define the sort of institution the Romans described. If we do, then by definition the production of children will be at the heart of it; and whatever else one may want to say about same-sex relationships, the production of children can hardly be said to be their purpose.