is known, though no details of his life before his accession are known. The earliest and most substantial source for Rædwald is the Historia ecclesiastica gentis Anglorum (Ecclesiastical History of the English People), completed in 731 by Bede, a Northumbrian monk. Bede placed Rædwald's reign between the advent of the Gregorian mission to Kent in 597 and the marriage and conversion of Edwin of Northumbria during 625–626. Later medieval chroniclers, such as Roger of Wendover, gave some information about East Anglian events, but Yorke suggests that the annalistic format used forced these writers to guess the dates of the key events they recorded. Such later sources are therefore treated with caution. The Anglian collection, which dates from the late 8th century, contains an East Anglian genealogical tally, but Rædwald is not included. Rædwald is however referred to in the 8th century Vita of St Gregory the Great, written by a member of the religious community at Whitby. The Battle of the River Idle, in which Rædwald and his forces defeated the Northumbrians, is described in the 12th century Historia Anglorum, written by Henry of Huntingdon. The context of Rædwald's kingdom The Anglo-Saxons, who are known to have included Angles, Saxons, Jutes and Frisians, began to arrive in Britain in the 5th century. By 600, a number of kingdoms had begun to form in the conquered territories. By the beginning of the 7th century, the southern part of what became England was almost entirely under their control. During Rædwald's youth, the establishment of other ruling houses was accomplished. Sometime before 588, Æthelberht of Kent married Bercta, the Christian daughter of the Frankish ruler Charibert I. As early as 568, Ceawlin of Wessex, the most powerful ruler south of the River Humber, repulsed Æthelberht. According to later sources, Mercia was founded by Creoda in 585, although a paucity of sources makes it difficult to know how the Mercian royal line became established. North of the Humber, the kingdoms of Deira and Bernicia possessed rival royal dynasties. Ælla ruled Deira until his death in 588, leaving his daughter Acha, his son Edwin, and another unknown sibling. The Bernician dynasty, allied by kinship to the kingdom of Wessex, gained ascendancy over Deira, forcing Edwin to live in exile in the court of Cadfan ap Iago of Gwynedd. In various wars, Æthelfrith of Bernicia consolidated the Northumbrian state, and in around 604 he was able