A defensive strategy becomes more apparent in the later part of Alfred's reign. It was built around the possession of fortified places and the close pursuit of the Danes to harass them and impede their preferred occupation of plundering. Alfred and his lieutenants were able to fight the Danes to a standstill by their repeated ability to pursue and closely besiege them in fortified camps throughout the country. The fortification of sites at Witham, Buckingham, Towcester and Colchester persuaded the Danes of the surrounding regions to submit. The key to this warfare was sieges and the control of fortified places. It is clear that the new fortresses had permanent garrisons, and that they were supported by the inhabitants of the existing burhs when danger threatened. This is brought out most clearly in the description of the campaigns of 917 in the "Chronicle", but throughout the conquest of the Danelaw by Edward and Æthelflæd it is clear that a sophisticated and coordinated strategy was being applied.