Wow- good question.
More important of a question is when they started to have *meaning* - before renaissance England (in the West), marriages were just arranged formalities.
Edmund Spencer (in The Fairie Queene - a masterpiece) made marriage a meaningful entity in Western culture. But beyond that, I think marriage was an important institution with Indian and Chinese cultures.
I don't consider Babylon or Egypt "marriages" because polygamy was the norm -