There was once a time when Scotland's rivers and glens teemed with hosts of supernatural creatures. Witches practiced their black arts along the craggy shorelines, their cackling drowned out in the roar of turbulent crashing waves. Inland, spirits of the restless dead flitted across the mist-covered moors. Monsters prowled through dark forests, waiting for a weary wanderer to devour while evil creatures lurked beneath choppy waters. One had to take care to tread lightly through certain places. Earthen mounds or small hills were especially dangerous, haunted as they were by the hill-folk. Daily life could be treacherous, filled with evil spirits that could whisk away children as they slept, strike whole herds of livestock with plague, cap-size fishing boats, and make mischief in homes as the family slept. Superstition was particularly strong in the northern areas and the islands, where Scandinavian folklore had deeply penetrated the indigenous cultures. The Scots could scarcely find a place that was free of supernatural influence, so rich was their folk tradition.
As Christianity subsumed the Norse, Celtic, and Brythonic cultural mixture of medieval Scotland, it transformed old folkloric elements to reflect the shift in religious belief. Rather than usurp native folk tradition, Christianity simply provided new explanations for old beliefs. Instead of casting the multitude of supernatural creatures out of Scotland's rivers and glens, the new religion used its own folkloric pantheon to assimilate them.
When Lucifer waged war against God in heaven, some of the angels rebelled with him while others remained righteous and rallied behind Saint Michael the Archangel. Others, however, remained neutral and did not fight on either side. Because they did not take up arms to fight for goodness and justice, Michael closed them out of the gates of Heaven. But because they had not rebelled against God, he did not cast them into Hell. Instead, these angels fell onto the earth. Those who landed on solid ground became the hill-folk, faeries and pixies, while those who crashed into the sea became selkies, Finfolk, or other creatures of the sea.