Soldiers throughout the country were summoned, for both offensive and defensive war; early armies consisted essentially of household bands, while later on men were recruited on a territorial basis. The mustering of an army, annually at times, occupied an important place in Frankish history, both military and constitutional. The English kingdoms appear to have known no institution similar to this. The earliest reference is Bede's account of the overthrow of the Northumbrian Æthelfrith by Rædwald overlord of the southern English. Rædwald raised a large army, presumably from among the kings who accepted his overlordship, and "not giving him time to summon and assemble his whole army, Rædwald met him with a much greater force and slew him on the Mercian border on the east bank of the river Idle." At the Battle of Edington in 878, when the Danes made a surprise attack on Alfred at Chippenham after Twelfth Night, Alfred retreated to Athelney after Easter and then seven weeks after Easter mustered an army at "Egbert's stone". It is not difficult to imagine that Alfred sent out word to the ealdormen to call his men to arms. This may explain the delay, and it is probably no more than coincidence that the army mustered at the beginning of May, a time when there would have been sufficient grass for the horses. There is also information about the mustering of fleets in the eleventh century. From 992 to 1066 fleets were assembled at London, or returned to the city at the end of their service, on several occasions. Where they took up station depended on the quarter from which a threat was expected: Sandwich if invasion was expected from the north, or the Isle of Wight if it was from Normandy.