829. Ecgberht of Wessex takes direct control over Mercia
Ecgberht of Wessex meets the Northumbrians and makes peace with them

The Anglo-Saxon Chronicle notes that Ecgberht conquered the kingdom of the Mercians. This is confirmed by an issue of coins of Ecgberht as king of the Mercians (with the inscription ECGBERHT REX M, for Rex Merciorum), and a regnal list of Mercia which assigns Ecgberht a reign of one year (see Keynes, "Alfred", p.4, and references there).

The Chronicle notes further that Ecgberht had conquered everything south of the Humber, and so was the eighth king who was Bretwalda, or Brytenwalda; the chronicler then inserts Bede's list of seven kings who held wide powers south of the Humber (HE, ii.5), and adds Ecgberht at the end. This annal has seemed to solidify the idea of overlordship over Southumbrian England into a recognized post, with attendant ramifications and questions (Was the "sceptre" found at Sutton Hoo the symbol of Rædwald's "Bretwalda-ship"? Why are the Mercian overlords from Penda to Offa not counted as "Bretwaldas" number 8-12, making Ecgberht the 13th?). It seems more likely, however, that the word was invented by the chronicler than that it was a long-recognized official title. It appears elsewhere only once, in a forged charter of King Æthelstan (S 427; not even the 9th-century Old English translation of Bede uses "Bretwalda"), and the copyists of the Chronicle seem unsure what the word is (different manuscripts use three different words, Bretwalda, Brytenwalda, and Brytenanwalda; see further Keynes, "Bretwalda", pp.110-16).

After Ecgberht conquered the Mercians, the Chronicle reports that he led an army to Dore (in northern Derbyshire) against the Northumbrians, and they submitted to him there and made peace with him, and parted on those terms. Roger of Wendover in the 13th century writes that Ecgberht took a large army into Northumbria and ravaged the province and made King Eanred pay tribute, but this contradicts earlier accounts and one might expect the Chronicle written in the reign of Ecgberht's grandson to make more of such a conquest if it had taken place.

S. Keynes, "Rædwald the Bretwalda", Voyage to the Other World: The Legacy of Sutton Hoo (Minneapolis: 1992), pp.103-23

S. Keynes, "King Alfred and the Mercians", in M. Blackburn and D. Dumville (edd.), Kings, Currency and Alliances: History and Coinage of Southern England in the Ninth Century (Woodbridge: 1998), pp.1-45