In 626, according to the Anglo-Saxon Chronicle: "This year Penda succeeded to the kingdom [of Mercia] and reigned thirty winters." As king of Mercia Penda's first victory came in 628. The Anglo-Saxon Chronicle for 628 says that Cyngils, king of Wessex, and Cwichelm his son 'fought with Penda at Cirencester and came to an agreement with him there'. The 'agreement' seems to have been to give Cirencester to Penda. It's likely Penda also got the territory of the Hwicce at this time. The agreement or treaty also seems to have been a marriage alliance. Penda married Cynewise, probably a sister of Cynegils. He formed an alliance with Cadwallon ap Cadfan of Gwynedd. Cadwallon was known to have been very hostile towards the Northumbrians. In 633 Penda joined him in invading Northumbria. At Battle of Hatfield Chase their combined armies defeated and killed King Edwin of Northumbria. Cadwallon remained in Northumbria for a year destroying everything he could. Penda left and returned to Mercia. He brought with him Eadfrith, the son of Edwin, as a prisoner possibly to set up as a puppet ruler in Northumbria under Penda. But Penda had him murdered a few years later. 