I hate the phrase "traditional marriage." I think if you're going to use it, you need to clarify traditional as compared to what? 1950? 1920s? 1800s? Middle Ages? Biblical times?
Marriage is an institution that has evolved and will continue to evolve both culturally and legally. Marriage today looks different than it did 50 or 100 or a 1000 years ago. Not just in regards to societal expectations but also in regards to a woman's legal status and rights as a person.
Marriage in biblical times sometimes meant that a husband took multiple wives, or perhaps one wife but with many concubines (which was not hidden or frowned upon) or that teenage girls were married off to much older men. Also, most marriages were arranged and treated like a transaction, which involved a dowry. Heterosexual monogamy where one chooses his/her spouse is a relatively new normal standard if we're comparing it to as far back as we have records regarding marriage.
Good sources for more information on this include The History of the Wife, anything by Stephanie Coontz (author/history & family studies professor), or the Bible. I'm sure there's many more as well that I'm not aware of.
I get really exasperated when people act like marriage has looked one specific way since the history of time because that is clearly not the case.