During the 9th century, Wessex rose in power, from the foundations laid by King Egbert in the first quarter of the century to the achievements of King Alfred the Great in its closing decades. The outlines of the story are told in the "Anglo-Saxon Chronicle", though the annals represent a West Saxon point of view. On the day of Egbert's succession to the kingdom of Wessex, in 802, a Mercian ealdorman from the province of the Hwicce had crossed the border at Kempsford, with the intention of mounting a raid into northern Wiltshire; the Mercian force was met by the local ealdorman, "and the people of Wiltshire had the victory". In 829, Egbert went on, the chronicler reports, to conquer "the kingdom of the Mercians and everything south of the Humber". It was at this point that the chronicler chooses to attach Egbert's name to Bede's list of seven overlords, adding that "he was the eighth king who was Bretwalda". Simon Keynes suggests Egbert's foundation of a 'bipartite' kingdom is crucial as it stretched across southern England, and it created a working alliance between the West Saxon dynasty and the rulers of the Mercians. In 860, the eastern and western parts of the southern kingdom were united by agreement between the surviving sons of King Æthelwulf, though the union was not maintained without some opposition from within the dynasty; and in the late 870s King Alfred gained the submission of the Mercians under their ruler Æthelred, who in other circumstances might have been styled a king, but who under the Alfredian regime was regarded as the 'ealdorman' of his people.