Under Athelwulf's rule the ealdormen, the most important leaders after the king, became very important. In the 840s when viking raids became more frequent it was his ealdormen who led various local armies against the invaders. In 851 there were three large raids in southern England. The largest had over three hundred ships. They attacked at a place called Acleah in Surrey. Athelwolf and his son Athelbald met the Danes (vikings) in battle and defeated them. After this victory Athelwulf was considered the leading Anglo-Saxon king in England. In 852 Burghred of Mercia, a vassal king, asked for Athelwulf's help against Wales. Athelwulf did help and together they defeated Cyngen ap Cadell. Shortly afterward his daughter, Athelswith, became Burgred's wife and queen. By early 854 Athelwulf's wife, Osburgh, died. His eldest son Athelstan died about this same time.