fewer than three kings, two jarls and seven holds being slain. In fact this victory marks the beginning of the reconquest of the Danelaw.
Shortly after Duke Aethelred died, leaving only a daughter to carry on his line. At the moment his decease made little difference, for his widow Aethelfleda took up the reins of government without opposition, and for nearly eight years (912-919) led the Mercian forces with a skill and energy which few women rulers have ever equalled. In the scanty annals of these years, which speak of her regularly as "the Lady of the Mercians," she is always described as the directing mind, and we are not told the names of the men who assisted her, but one cannot help suspecting that at her right hand there really stood her nephew Aethelstan, the heir to the throne of Wessex, who is known to have been fostered and trained in the arts of ruling by Aethelred. For if this supposition may be hazarded, it will account for the ease with which the Mercian heiress was set aside after Aethelfleda's death, and also for the fact that, when Aethelstan came to be king, he seems to have been as much at home in Mercia as in his ancestral dominions. At any rate throughout Aethelfleda's period of power there was complete accord between herself and her brother, and her first step was to arrange that Edward should take over the defence of the districts that owed obedience to London and Oxford, these being much more easily protected from Wessex than from the Severn Valley. And then began a long-sustained campaign, carried on over several years by the sister and brother in conjunction, with the avowed object of expanding their territories, Edward acting against the Danes from the south and Aethelfleda from the west. Their plan evidently was to keep cautiously moving forward on a regular system, erecting "boroughs" as they went along their frontiers, as Alfred had done in Wessex, to secure their base should they at any moment be forced to draw back. In 913 for example Aethelfleda prepared for an advance in the Trent Valley by erecting boroughs at Stafford and Tamworth, and Edward for an advance in Essex by building two others at Hertford and Witham. In 914 the Danes retaliated by a raid on Luton and a foray into Mercian Cilternsaete as far as Hook Norton, both of which were easily repulsed by Edward, while further north Aethelfleda fortified Warwick in ancient Mercia and Eddisbury in Westerna. In 915 the appearance of a force of vikings from Brittany in the Severn mouth caused some diversion, but Buckingham in Danish Cilternsaete was fortified none the less, and this led next year to the flight of Thurkytel, jarl of Bedford and the capture of his borough.
During these events, some of Aethelfleda's energy was being expended on her Welsh frontiers. We hear of a borough which she built at Chirbury in Shropshire and of an expedition into Brecknock; but in 917 she returned to the prosecution of the main scheme and got possession of Derby. This meant that the armies of Northampton and Leicester were placed between two fires, and it convinced their jarls that
