In 879 a Viking fleet that had assembled in the Thames estuary sailed across the channel to start a new campaign on the continent. The rampaging Viking army on the continent encouraged Alfred to protect his Kingdom of Wessex. Over the following years Alfred carried out a dramatic reorganisation of the government and defences of Wessex, building warships, organising the army into two shifts which served alternately and establishing a system of fortified "burhs" across the kingdom. This system is recorded in a 10th-century document known as the Burghal Hidage, which details the location and garrisoning requirements of thirty-three forts, whose positioning ensured that no one in Wessex was more than a long day's ride from a place of safety. In the 890s these reforms helped him to repulse the invasion of another huge Danish army – which was aided by the Danes settled in England – with minimal losses.