 Complete the following phrase:  Roman military withdrawals left Britain open to invasion by pagan, seafaring warriors from north-western continental Europe, chiefly the Saxons, Angles, Jutes and Frisians who had long raided the coasts of the Roman province. These groups then began to settle in increasing numbers over the course of the fifth and sixth centuries, initially in the eastern part of the country. Their advance was contained for some decades after the Britons victory at the 