917. Edward builds fortresses at Towcester and Wigingamere
Much campaigning: Edward receives submissions of armies of Northampton, East Anglia, Cambridge
Æthelflæd takes the borough of Derby (one of the Five Boroughs)
In 917, before Easter, Edward ordered a fort built at Towcester (which would block the southern advance of Danes from Northampton), and another at Wigingamere (unidentified).
In the summer, the Danes of Northampton and Leicester and the area to the north stormed the new fort at Towcester but were repelled; they then successfully raided a less well-protected area, near Aylesbury. Meanwhile, the Danish army of Huntingdon and East Anglia built a fortress at Tempsford, some ten miles south of Huntingford, abandoning Huntingford because Tempsford was closer to the English border. The Danes of Tempsford attacked the nearby English fortress at Bedford, but were repulsed. Another Danish army from East Anglia and Mercia gathered, and attacked the fortress at Wigingamere, but were repulsed.
In the English counterattack, Edward gathered an army and attacked the Danish fortress at Tempsford and took it by storm, killing the king and Earl Toglos and his son, Earl Manna. Another English host assembled in the autumn from Kent, Surrey, and Essex and the nearest fortresses on all sides, and besieged the Danish fortress of Colchester and took that and killed all the people within.
In the autumn, an army of East Anglians and Vikings went to Maldon and attacked the fortress, but more English troops came from outside, and the Danes were put to flight. (This East Anglian army may have been fragmenting, since their king and many nobles had been killed at Tempsford.)
Shortly afterwards, in that same autumn, Edward brought the army of the West Saxons to Passenham, and stayed there while the fortress of Towcester was given a stone wall. Then Earl Thurferth submitted to him, as did the army of Northampton. The English army went on to restore the fortresses at Huntingdon and Colchester (abandoned by and taken from the Danes earlier in the year), and many of the people who had been under Danish rule in East Anglia and Essex submitted to him, as did the Danish army in East Anglia, and the army of Cambridge.
These decisive English victories are partly the result of the system of fortifications that had been perhaps a decade (counting from the restoration of Chester in 907) in the making, and partly also of the fact that the Danes were actually under attack from both sides. While Edward was holding the southward advance from the Five Boroughs and advancing westwards from East Anglia, his sister Æthelflæd took Derby, one of the Five Boroughs, and all that belonged to it. The Mercian annals report that this took place before Lammas (August 1).