Our lack of knowledge about the history of marriage traditions makes sense considering their roots can be traced back to multiple cultures and eras, each one adopting a piece of the ritual to pass down.
Take the tradition of wearing the wedding ring on the left hand for example- this tradition can be traced back to ancient Egypt, but may have become part of the modern marriage tradition thanks to the Romans:
The union between marriage and the now-standard ring placement can be traced back to second-century Egyptians who falsely believed that “a certain most delicate nerve” began in the fourth left finger and stretched directly to the heart, according to the Greek scholar Appian. Centuries later, the Romans came to a similar conclusion. In place of a nerve, they were convinced that a vena amoris—or “lover’s vein”—connected this digit with the blood-pumping organ.
During the Roman engagement process, a well-off suitor who could afford a ring would slip it over his bride-to-be’s fourth finger. Thus, he’d always have a symbolic grip around her lover’s vein. The modern world may have adopted that practice from the Romans.