Edward continued his wars against the Danes. He received a great deal of aid from his sister, Ethelflaeda. She had married Ethelred of Mercia and at his death she became the leader of the Mercians. Together Edward and Ethelflaeda defeated the Danes in numerous battles. But Ethelflaeda also built a line of fortresses on the Mercian Frontier. This was what her father Alfred the Great had done on the Wessex borders with the Danish held territories. Edward began to use these fortresses differently. Not just for defense of his own lands he used them to hold captured lands. Edward and his sister were very successful against the Danes. So much so they quit raiding into Wessex and Mercia. Freed of wars with the Daneds, Edward could attend to other issues. He brought Strathclyde and parts of Northumbria under his control. He also brought Mercia under his direct rule after his sister Ethelflaeda died. The appearance of the Viking leader Ragnvald in York slowed his progress. But by the end of his reign he had control of all lands south of the River Humber. In a treaty Ragnvald, the kings of Strathclyde and the Scots recognized his rule.