In 733 Somerton was lost to King Aethelbald of Mercia. This was quickly followed by the territory beyond Selwood being lost to Mercia. Athelheard's authority was so weak that Aethelbald was able to give the Archbishop of Canterbury a gift of the monastery of Cookham in Berkshire (Wessex). Aethelbald also took Wiltshire, Sussex and much of the heartlands of Wessex. Athelheard could do nothing to prevent this loss. He also took part in Athelbald's wars with the Welsh. It seems Athelbald's wife, Frithugyth, was Mercian herself. In 737 she made a pilgrimage to Rome along with bishop Forthhere of Sherborne. Athelheard died in 740, his successor was his kinsman Cuthred.