Northumbria was formed in the early 7th century by Athelfrith, King of Bernicia. He conquered the kingdom of Deira and several British kingdoms and combined them under his rule. The kingdom of Northumbria also included Lindsey at times. Northumbria was a part of the Heptarchy of Anglo-Saxon kingdoms. At its greatest the kingdom extended at least from just south of the Humber river, to the River Mersey and to the Forth (roughly, Sheffield to Runcorn to Edinburgh). The name 'Northumbria' wasn't in common use until the time of Ecgfrith, King of Northumbria. The name is first used in the preamble to the council of Hatfield (680). Ecgfrith was described as king of the Humberfolk'. After the loss of Lindsey (kingdom) which was south of the River Humber, the name became Northumbria in Latin is "Northanhymbrenis." It comes from the Old English "be northan Hymbre" meaning 'to the north of the Humber'. The name Northumbria was still used during the reigns of Kings Canute and Edward the Confessor. William the Conqueror broke up Northumbria into several parts. Yorkshire became the new name for the heartlands of the former kingdom.