 The extent of the kingdom of the East Angles can be determined from a variety of sources . Isolated to the north and east by the North Sea , there were mainly impenetrable forests to the south and the swamps and scattered islands of the Fens on its western border . The main land route from East Anglia would at that time have been a land corridor , along which ran the prehistoric Icknield Way . The southern neighbours of the East Angles were the East Saxons and across the other side of the Fens were the Middle Angles . It has been suggested that the Devil 's Dyke ( near modern Newmarket ) at one time formed part of the kingdom 's western boundary , but as its construction can only be dated from between the 4th and 10th centuries , it cannot be established to be of Early Anglo @-@ Saxon origin . 
