Here's an interesting review of the history of marriage. Or you could say "histories", as it's rather non-linear.
The relatively recent trend of state-recognized marriage has nothing to do with the idea of marriage as “natural” union under God and human nature. As Columbia University history professor Steven Mintz puts it: “Whenever people talk about traditional marriage or traditional families, historians throw up their hands. We say, ‘When and where?’” There is no such thing as “traditional marriage.” Different societies in different times have had very different marriage traditions.
But historically, until the Protestant Reformation, most European states didn’t recognize the marriages of anyone without assets—about 85 percent of the population. God may have created Adam and Eve, but the state only cared about ownership of the Garden of Eden.
In a lot of these instances the church - whatever church that might be - took up the slack for the majority of marriages. But the role of religious institutions hasn't been consistent either. So the idea of whether and how our ancestors were wed is complex and in some cases subjective.