The story of the apocryphal pope and saint Gregorius was extremely popular throughout the middle ages and later in Europe and beyond. In a memorable narrative Gregorius is born from an incestuous relationship between a noble brother and sister, and is set out to sea with (unspecific) details of his origin. He is found and brought up by an abbot, but when revealed as a foundling leaves as a knight to seek his origins; he rescues his mother's land from...