At the time of Alfred's death, and the succession of Edward the Elder to the crown (901), Ethelfleda, daughter of Alfred, was the wife of Ethelred, ealdorman of Mercia, who appears to have been a sort of under-king of that province.[32] On the death of Ethelred in 912,[33] Edward took possession of London and Oxford and "of all the lands which owed obedience thereto"--in other words, of that small portion of Eastern Mercia which was still in English hands; that is, not only the present Oxfordshire and Middlesex, but part of Herts, part of Bedfordshire, all Buckinghamshire, and the southern part of Northants. The Watling Street, which runs north-west from London to Shrewsbury, and thence north to Chester and Manchester, formed at that time the dividing line between the English and Danish rule.[34] It would seem from the course of the story that after Ethelred's death there was some arrangement between Ethelfleda and her brother, possibly due to the surrender of the territory mentioned above, which enabled her to rule English Mercia in greater independence than her husband had enjoyed. Up to this date we find Edward disposing of the _fyrd_ of Mercia;[35] this is not mentioned again in Ethelfleda's lifetime. Nothing is clearer, both from the _Chronicle_ and from Florence, than that the brother and sister each "did their own," to use an expressive provincial phrase. Ethelfleda goes her own way, subduing Western Mercia, while Edward pushes up through Eastern Mercia and Essex to complete the conquest of East Anglia. A certain concert may be observed in their movements, but they did not work in company. The work of fortification begun in Alfred's reign had been continued by the restoration of the Roman walls of Chester in 908, by Ethelred and his wife; and Ethelfleda herself (possibly during the lingering illness which later chroniclers give to her husband) had built a _burh_ at Bremesbyrig. During the twelve years which elapsed between Ethelred's death and that of Edward in 924, the brother and sister built no less than twenty-seven _burhs_, giving a total of thirty, if we add Chester and Bremesbyrig, and Worcester, which was built in Alfred's reign. Now what was the nature of these fortifications, which the _Anglo-Saxon Chronicle_ uniformly calls _burhs_? There is really not the slightest difficulty in answering this question. The word is with us still; it is our word _borough_. It is true we have altered the meaning somewhat, because a borough means now an enfranchised town; but we must remember that it got that meaning because the fortified towns, the only ones which were called _burhs_ or _burgi_, were the first to be enfranchised, and while the fortifications have become less and less important, the franchise has become of supreme importance.