 The strix appeared in classical Roman literature; it was described by the Roman poet Ovid, who was widely read in the Middle Ages, as a large-headed bird with transfixed eyes, rapacious beak, and greyish white wings.They were part of the visual message for the illiterate worshippers, symbols of the evil and danger that threatened those who did not follow the teachings of the church.The gargoyles, which were added to Notre-Dame in about 1240, had a more practical purpose.