, and the Kentish men, in a separate battle,
attacked and slew Eric their king with several of his earls. In 912,
AEthelred the Mercian died, and Eadward at once incorporated London and
Oxford with his own dominions, leaving his sister AEthelflaed only the
northern half of her husband's principality. Thenceforth AEthelflaed, "the
Lady of the Mercians," turned deliberately to the conquest of the North.
She adopted a fresh kind of tactics, which mark again a new departure in
the English policy. Instead of keeping to the old plan of alternate
harryings on either side, and precarious tenure of lands from time to
time, AEthelflaed began building regular fortresses or _burhs_ all along
her north-eastern frontiers, using these afterwards as bases for fresh
operations against the enemy. The spade went hand in hand with the
sword: the English were becoming engineers as well as fighters. In the
year of her husband's death, the Lady built _burhs_ at Sarrat and
Bridgnorth. The next year "she went with all the Mercians to Tamworth,
and built the _burh_ there in early summer; and ere Lammas, that at
Stafford." In the two succeeding years she set up other strongholds at
Eddesbury, Warwick, Cherbury, Wardbury, and Runcorn. By 917, she found
herself strong enough to attack Derby, one of the chief cities in the
Danish confederacy of the Five Burgs, which she captured after a hard
siege. Thence she turned on Leicester, which capitulated on her
approach, the Danish host going over quietly to her side. She was in
communication with the Danes of York for the surrender of that city,
too, when she died suddenly in her royal town of Tamworth, in the year
918.

Meanwhile Eadward had been pushing forward his own boundary in the east,
building _burhs_ at Hertford and Witham, and endeavouring to subjugate
the Danish league in Bedford, Huntingdon, and Northampton. In 915,
Thurketel, the jarl of Bedford, "sought him for lord," and Eadward
afterwards built a _burh_ there also. On his sister's death, he annexed
all her territories, and then, in a fierce and long doubtful struggle,
reconquered not only Huntingdon and Northampton but East Anglia as well.
The Christian English hailed him as a deliverer. Next, he turned on
Stamford, the Danish capital of the Fens, and on Nottingham, the
stronghold of the Southumbrian host. In both towns he erected _burhs_.
These successes once more placed the West Saxon king in the foremost
position amongst the many rulers