Marriage as a religious institution is less than 500 years old. It was only with the council of trent in 1547 that marriage became officially tied to the catholic church. Of course there were priests irregularly involved in marriages before then, but priests were involved in everything, marriage had as much religious significance as harvesting your grain, or curing the sick, which priests were also involved in.however, i don't support it being called a 'marriage'. the simple fact is that marriage has been the term that has denoted a bond between a man and a woman for thousands of years. as much as i think religious people are bat shit insane, the word marriage has large religious connotations and a lot of tradition to it.
Martin luther, icon of the protestant reformation, actually campaigned against church involvement in marriage, calling it a 'wordly thing'. As a result, the English parliament banned church involvement in marriage for a time in the 17th century. The notion of seperation of church and marriage was also influential on the American puritans at the time.