From Gary Wills’ new article at New York Review of Books:

The early church had no specific rite for marriage. This was left up to the secular authorities of the Roman Empire, since marriage is a legal concern for the legitimacy of heirs. When the Empire became Christian under Constantine, Christian emperors continued the imperial control of marriage, as the Code of Justinian makes clear. When the Empire faltered in the West, church courts took up the role of legal adjudicator of valid marriages. But there was still no special religious meaning to the institution. As the best scholar of sacramental history, Joseph Martos, puts it: “Before the eleventh century there was no such thing as a Christian wedding ceremony in the Latin church, and throughout the Middle Ages there was no single church ritual for solemnizing marriage between Christians.”