As king of Wessex at the age of 21, Alfred (reigned 871-99) was at the head of remaining resistance to the Vikings in southern England. In early 878, the Danes led by King Guthrum seized Chippenham in Wiltshire in a lightning strike and used it as a secure base from which to devastate Wessex.  With only his royal bodyguard, a small army of thegns, and Aethelnoth, earldorman of Somerset as his ally, Alfred withdrew to the Somerset tidal marshes. A resourceful fighter, Alfred reassessed his strategy and pursued guerrilla warfare against the Danes. In May 878, Alfred's army defeated the Danes at the battle of Edington.  This unexpected victory proved to be the turning point in Wessex's battle for survival.

Realising that he could not drive the Danes out of the rest of England, Alfred concluded peace with them in the treaty of Wedmore. King Guthrum was converted to Christianity with Alfred as godfather and many of the Danes returned to East Anglia where they settled as farmers. In 886, Alfred negotiated a partition treaty with the Danes, in which a frontier was demarcated along the Roman Watling Street and northern and eastern England came under the jurisdiction of the Danes - an area known as 'Danelaw'. Alfred therefore gained control of areas of West Mercia and Kent which had been beyond the boundaries of Wessex. To consolidate alliances against the Danes, Alfred married one of his daughters, Aethelflaed, to the ealdorman of Mercia -Alfred himself had married Eahlswith, a Mercian noblewoman - and another daughter, Aelfthryth, to the count of Flanders, a strong naval power at a time when the Vikings were settling in eastern England.

 Alfred started a building programof well-defended settlements across southern England. These were fortified market places where settlers received plots and in return manned the defences in times of war.  Centred around Alfred's royal palace in Winchester, this network of burhs with strongpoints on the main river routes was such that no part of Wessex was more than 20 miles from the refuge of one of these settlements. Together with a navy of new fast ships built on Alfred's orders, southern England now had a defence in depth against Danish raiders.

Alfred  recognized that the general deterioration in learning and religion caused by the Vikings' destruction of monasteries  had serious implications. To improve literacy, Alfred arranged, and took part in, the translation from Latin into Anglo-Saxon of a handful of books covering history, philosophy and Gregory the Great's 'Pastoral Care' (a handbook for bishops), and copies of these books were sent to all the bishops of the kingdom. Alfred was also patron of the Anglo-Saxon Chronicle, a patriotic history of the English from the Wessex viewpoint designed to inspire its readers and celebrate Alfred and his monarchy.

Alfred established a legal code; he assembled the laws of Offa and other predecessors, and of the kingdoms of Mercia and Kent, adding his own administrative regulations to form a definitive body of Anglo-Saxon law. By the 890s, Alfred's charters and coinage, which he had also reformed, extending its minting to the burhs he had founded, referred to him as "king of the English", and Welsh kings sought alliances with him. Alfred died in 899, aged 50, and was buried in Winchester, the burial place of the West Saxon royal family.

By stopping the Viking advance and consolidating his territorial gains, Alfred had started the process by which his successors eventually extended their power over the other Anglo-Saxon kings; the ultimate unification of Anglo-Saxon England was to be led by Wessex. It is for his valiant defence of his kingdom against a stronger enemy, for securing peace with the Vikings and for his farsighted reforms in the reconstruction of Wessex and beyond, that Alfred - alone of all the English kings and queens - is known as 'the Great'.