Bede's Ecclesiastical History of England, ed. by A.M. Sellar, , at sacred-texts.com
When the army of the enemy, having destroyed and dispersed the natives, had returned home to their own settlements, the Britons began by degrees to take heart, and gather strength, sallying out of the lurking places where they had concealed themselves, and with one accord imploring the Divine help, that they might not utterly be destroyed. They had at that time for their leader, Ambrosius Aurelianus, a man of worth, who alone, by chance, of the Roman nation had survived the storm, in which his parents, who were of the royal race, had perished. Under him the Britons revived, and offering battle to the victors, by the help of God, gained the victory. From that day, sometimes the natives, and sometimes their enemies, prevailed, till the year of the siege of Badon-hill, when they made no small slaughter of those enemies, about forty-four years after their arrival in England. But of this hereafter.