[All]: The notion of deception derives from the tradition that when Vortigern invited a select corps of Saxons to protect his kingdom they seized the opportunity to conquer the country, despite oaths to the contrary (Bede HE I, 15: Colgrave and Mynors 1969, 50-1; cf. Henry of Huntingdon, largely quoting Bede, in HA 1996, 80-1).