Throughout most of history the act of being "married" in Western culture was very informal. It didn't even become recognized as a sacrament in the Roman Catholic rite until the Middle Ages.
And then often only formally celebrated among the nobility & royalty, with witnesses because of the great property and political issues involved. But it wasn't the near-coronation we see today in cathedrals, rather often a relatively small & private ceremony, even for Kings & Queens.
And among the common people there was virtually no ceremony at all, just a recognition & blessing by the local parish priest. Who made it official by personally entering the names into the church registry (since it was likely he was one of the few people within a village who could write).
And more pertinent to the issue of natural vs. unnatural, same-sex marriage was recognized by the Church during the late Roman period and into the early Middle Ages (aka the Dark Ages). Only later was it suppressed, and its memory erased as Church doctrine became hostile to the concept.