Aethelbald began taking over parts of Wessex. He obtained Berkshire in 730. Three years later he took Somerton from Wessex. Aethelbald was able to give the Archbishop of Canterbury a gift of the monastery of Cookham in Berkshire (Wessex). By 731 as Bede was finishing his "Ecclesiastical History", Aethelbald was overlord of all the English kingdoms south of the River Humber. In 740 Aethelbald burned York and destroyed much of Northumbria. The same year Athelheard of Wessex died and was replaced on the throne by Cuthred. Cuthred made it known he was not as weak a ruler as Athelheard and struggled against Aethelbald being his overlord. In the first three years of Cuthred's rule he warred with Mercia but made few gains. In 743 Cuthred joined Aethelbald in fighting the Welsh. In 748 Cuthred's son, Cynric, tried to his father and died in the rebellion. According to the Anglo-Saxon Chronicle, the rebellion was encouraged by Aethelbald. In 752, Cuthred tried to break free of King Aethelbald. This led to a battle at Burford where Cuthred battled against Aethelbald. The battle ended up with Aethelbald fleeing the battlefield. From that time on Cuthred maintained independence from Mercia for the rest of his reign.