Æthelflæd. Saintly relics were believed to give supernatural legitimacy to rulers' authority, and Æthelflæd was probably responsible for the foundation or re-foundation of Chester Minster and the transfer to it of the remains of the seventh-century Mercian princess Saint Werburgh from Hanbury in Staffordshire. She may also have translated the relics of the martyred Northumbrian prince Ealhmund from Derby to Shrewsbury. In 910 the Danes retaliated against the English attack of the previous year by invading Mercia, raiding as far as Bridgnorth in Shropshire. On their way back they were caught by an English army in Staffordshire and their army was destroyed at the Battle of Tettenhall, opening the way for the recovery of the Danish Midlands and East Anglia over the next decade. Lady of the Mercians On her husband's death in 911, Æthelflæd became Myrcna hlædige, "Lady of the Mercians". Ian Walker describes her succession as the only case of a female ruler of a kingdom in Anglo-Saxon history and "one of the most unique events in early medieval history". In Wessex, royal women were not allowed to play any political role; Alfred's wife was not granted the title of queen and was never a witness to charters. In Mercia, Alfred's sister Æthelswith had been the wife of King Burgred of Mercia; she had witnessed charters as queen and had made grants jointly with her husband and in her own name. Æthelflæd benefited from a Mercian tradition of queenly importance, and was able to play a key role in the history of the early tenth century as Lady of the Mercians, which would not have been possible in Wessex. When Æthelred died, Edward took control of the Mercian towns of London and Oxford and their hinterlands, which Alfred had put under Mercian control. Ian Walker suggests that Æthelflæd accepted this loss of territory in return for recognition by her brother of her position in Mercia. Alfred had constructed a network of fortified burhs in Wessex, and Edward and Æthelflæd now embarked on a programme of extending them to consolidate their defences and provide bases for attacks on the Vikings. According to Frank Stenton, Æthelflæd led Mercian armies on expeditions, which she planned. He commented: "It was through reliance on her guardianship of Mercia that her brother was enabled to begin the forward movement against the southern Danes which is the outstanding feature of his reign". Æthelflæd had already