In 865 a massive fleet arrived that carried some of the fiercest Viking leaders, including sons of the Danish King Ragnar Lodbrok ("Hairy-Breeches"), whose family was regarded as representing the very epitome of true Vikings. Ivar the Boneless, Halfdan, and Ubbi (or 'Hubba') brought military ambitions with them. Ragnar's sons captured York at the end of 867; and then proceeded to overrun most of Northumbria, Anglia, and Mercia. Ivar advanced to Dublin to conquer it, later dying in the Battle of Ashdown in 871. Halfdan became the chief leader following Ivar, where he defeated the English at Basing, Meretun, Reading, and Wilton. For the next few years the Vikings concentrated on securing conquests in eastern and northern England. They divided Northumbria and Mercia amongst themselves, and Halfdan followed in Ivar's footsteps in another attempt to secure Dublin from Ireland, only to be defeated by Norwegian Vikings in 877. The Scandinavian countries seemed to possess an inexhaustible supply of able-bodied warriors and manpower. In land battles Vikings favored overlapping shield-wall formations, which consisted of approximately 5 or more ranks deep of the most heavily armed and armored Vikings forming the exterior of a line, wedge, or circle formation to absorb the brunt of enemy attacks. In the pagan era, before Scandinavia was converted to Christianity, the berserkir warriors were looked upon as possessing supernatural powers attributed to the Viking's chief god, Odin; and a belief in lycanthropy. These warriors were known to rush into battle without armor, as mad as wolves, and as strong as wild boars. This infamous berserkir frenzy reportedly allowed them to kill men in single blows with great bearded axes, and shrug off blows from fire and iron alike. Today it is believed that these frenzies were the result of epileptic attacks. The era of the Viking lasted only 300 years, ending at approximately 1066AD; around the time of the approximated death of Harald Hardrada, who died heroically in battle. Harald has been dubbed 'the last Viking'. Most remaining Viking conquests and exploits never amounted to those of their predecessors, and Viking lineage gradually integrated into their surrounding civilizations.