In the early Middle Ages all it took for a couple to wed was an exchange of promises between the two people who wished to wed. This exchange did not need to be public nor did it require witness. Needless to say this frequently resulted in "He said - She said" situations.
Ninth century Frankish law recognized two types of marriage: Muntehe and Friedelehe. Muntehe was a permanent and formal marriage where the bride was "given" to the groom. Friedelehe was less formal and more of a "loan" of the bride with no transfer of property or authority to the groom. Offspring of a Friedelehe marriage were entitled to inherit if there were no heirs from a Muntehe marriage.
In 1076 the Council of Westminster declared "no man shall give his daughter or female relative to anyone without priestly blessing."
The Fourth Lateran Council of 1215 proclaimed it necessary for marriage to be blessed and witnessed by clergy. It also required the publication of Marriage Banns (a public announcement of the intent to marry asking for testimony of consanguinity (degree of relatedness), eligibility (availability, age or consent). Contrary to their own proclamations, the church continued to recognize "clandestine marriages" (those made without benefit of clergy) as late as the 18th century. Prior to the Lateran Council the presence of clergy at a weddings was rare.
During the Reformation, Martin Luther argued that marriage was "a worldly business" where "we clergy ought not to meddle." He did, however, agree that clergy should bless marriage and in 1529 presented a basic marriage rite for the church.
In response to the Reformation, the Council of Trent issued a decision against clandestine marriage in 1563. The Council declared for a marriage to be recognized by the Church, legal and binding it must be 1) public, 2) consensual, and 3) witnessed and blessed by the Church.