The mutations of marriage in the eleventh and twelfth century.
A somewhat difficult matter to trace, because all the records, of course, come from priests, bishops, and other clerks. Which is to say, from one side of the marriage debate. The nobles wanted to go merrily on with their own practices, including abduction, repudiation, and concubinage. And the clergy, many of whom were not too keen on this whole sex business, were trying to drag into somewhat in conformity into their own notions of proper marriage.
They won, on the whole. Abduction steadily decreased, no doubt aided by rules that a betrothed woman, at least, could not marry her abductor. Repudiating a wife first revolved around claims of adultery, since a man could repudiate her on his oath that she had, but it had the disadvantage that bishops who were willing for them to separate were not as willing to permit a remarriage. (For the man. Since women were weak and licentious beings, they found it much easier to remarry.) They went for incest next, especially since the Church had set absurdly wide relations for incest, and indeed was more often complaining of incestuous unions when the same unions were also bigamous; when the Church cranked them down, many people were quite unhappy. But repudiations, even of barren wives, definitely declined.
Even the marriage ceremonies changed. In the beginning, they -- for those with property -- consisted of a formal reading of the documents where the property arrangements were set out, and a rather frolicsome conducting the bride to her marriage bed. The Church introduced a blessing between them -- perhaps aping royalty, where the bride had to be crowned queen -- and then the marriage vows, which had, of all things, to be spoken by the bridegroom and the bride themselves. And then they insisted that it was the vows that did it. . . which meant that some concubines were declared wives, not chance lovers, since the man and woman had joined together of their will.
It was a troubled time. There were a lot of heresy afloat, many of which revolved about marriage and regarding it as intrinsically sinful. And therefore were notorious for their sexual practices, because if there was no licit way to engage in sexual intercourse, you might as well go whole hog.