It is often claimed that marriage has always been between a man and woman. For example:

I see this as an argument over the definition of a word – marriage = man and woman, and has done since the word was ‘created’

Definitions include:

1. to take in marriage

2. to perform the marriage ceremonies for (two people); join in wedlock.

3. to give in marriage; arrange the marriage of.

4. to unite intimately: Common economic interests marry the two countries.

5. to take as an intimate life partner by a formal exchange of promises in the manner of a traditional marriage ceremony.

Where does the word ‘marry’ come from?

Origin:
1250–1300; Middle English marien < Old French marier < Latin marītāre to wed, derivative of marītus conjugal, akin to mās male (person)

Word Origin & History
marry
c.1300, from O.Fr. marier, from L. maritare “to wed, marry, give in marriage,” from maritus “married man, husband,” of uncertain origin, perhaps ult. from “provided with a *mari,” a young woman, from PIE base *meri- “young wife,” akin to *meryo- “young man” (cf. Skt. marya- “young man, suitor”).

marry
a common oath in the Middle Ages, c.1350, now obsolete, a corruption of the name of the Virgin Mary.

http://dictionary.reference.com/browse/marry

Nothing there definitively saying marriage = man and woman. It seems to be man orientated, not surprising as marriage often used to be man owns woman (as part of his property). A marriage was a convention used to breed an heir for his property.

And anyone who knows about language evolution will say the definition history is irrelevant. “Gay” has evolved to a variety of modern uses, eg merry, homosexual and lame.

As others have said, how we legally define marriage is up to us now.

It could be said that Louisa Wall is trying to make marry merry.