This is dependent upon the local parish church. During the Middle Ages, it was widely believed that evil spirits could be released from hell by Satan to spoil the union God had created. It was also believed, however, that the color white was impenetrable by such evil spirits. To protect the bride and groom, the white aisle runner was often used for weddings. Today, the runner can be a way of protecting the bridal gown. Or, it can be a tripping hazard.