The word for today is PRELIMINARY which comes from the Latin words pre = before, and limen = threshold.
The custom of carrying the bride over the threshold has its origin in ancient Rome. It was tradition that the groom’s parents supply the newlyweds with animal fat and oil. The purpose of the animal fat was for cooking and the oil was used to keep the lanterns in the couple’s new house lit.
Since Romans were deeply superstitious it was believed that the house the married couple moved into must be blessed so the marriage would prosper. The practice that came to be was that the groom would rub animal fat around the entrance of the door and when the bride would first have to enter the house he must carry her over so that she would not slip. It was thought that if the bride did not slip the house would always contain plenty of animal fat for cooking and oil for burning, but if the bride slipped, the house and couple were doomed to misfortune.