According to Gildas, initial vigorous British resistance was led by a man called Ambrosius Aurelianus, from which time victory fluctuated between the two peoples. Gildas records a "final" victory of the Britons at the Battle of Mount Badon in c. 500, and this might mark a point at which Anglo-Saxon migration was temporarily stemmed. Gildas said that this battle was "forty-four years and one month" after the arrival of the Saxons, and was also the year of his birth. He said that a time of great prosperity followed. But, despite the lull, the Anglo-Saxons took control of Sussex, Kent, East Anglia and part of Yorkshire; while the West Saxons founded a kingdom in Hampshire under the leadership of Cerdic, around 520. However, it was to be 50 years before the Anglo-Saxons began further major advances. In the intervening years the Britons exhausted themselves with civil war, internal disputes, and general unrest, which was the inspiration behind Gildas's book "De Excidio Britanniae" (The Ruin of Britain).