 Complete the following phrase:  Arthur is not mentioned in Gildas 6th-century book De Excidio et Conquestu Britanniae. Gildas does mention a British victory against the Saxons at the Badonic mount mons Badonicus, which occurred in the year of Gildas birth and ushered in a generation of peace between the two warring peoples. This engagement is now referred to as the 