But all this literary activity was only a part of that general upbuilding of Wessex by which AElfred was preparing for a fresh contest with the stranger. He knew that the actual winning back of the Danelaw must be a work of the sword, and through these long years of peace he was busy with the creation of such a force as might match that of the northmen. A fleet grew out of the little squadron which AElfred had been forced to man with Frisian seamen. The national fyrd or levy of all freemen at the King's call was reorganized. It was now divided into two halves, one of which served in the field while the other guarded its own burhs and townships and served to relieve its fellow when the men's forty days of service were ended. A more disciplined military force was provided by subjecting all owners of five hides of land to thegn-service, a step which recognized the change that had now substituted the thegn for the eorl and in which we see the beginning of a feudal system. How effective these measures were was seen when the new resistance they met on the Continent drove the northmen to a fresh attack on Britain. In 893 a large fleet steered for the Andredsweald, while the sea-king Hasting entered the Thames. AElfred held both at bay through the year till the men of the Danelaw rose at their comrades' call. Wessex stood again front to front with the northmen. But the King's measures had made the realm strong enough to set aside its old policy of defence for one of vigorous attack. His son Eadward and his son-in-law AEthelred, whom he had set as Ealdorman over what remained of Mercia, showed themselves as skilful and active as the King. The aim of the northmen was to rouse again the hostility of the Welsh, but while AElfred held Exeter against their fleet, Eadward and AEthelred caught their army near the Severn and overthrew it with a vast slaughter at Buttington. The destruction of their camp on the Lea by the united English forces ended the war; in 897 Hasting again withdrew across the Channel, and the Danelaw made peace. It was with the peace he had won still about him that AElfred died in 901, and warrior as his son Eadward had shown himself, he clung to his father's policy of rest. It was not till 910 that a fresh rising of the northmen forced AElfred's children to gird themselves to the conquest of the Danelaw. [Sidenote: Eadward the Elder]