Harald Fairhair was the first king of all Norway, bringing the lands of what had previously been several distinct petty-kingdoms under his control. The foundation of this unified Norwegian kingdom is traditionally dated to 872, when he defeated the last petty kings who resisted him at the Battle of Hafrsfjord, though the consolidation of his power took many years. Fairhair's kingdom spanned the coastal areas north to Trøndelag, but upon his death the kingship was fragmented back into the petty kingdoms, most being held by Harald's sons, descendants or allies, though there were also districts in the hands of other dynasties, such as Ladejarls. Nonetheless, the concept of control by a central power had come into existence. It remains disputed the degree to which Norway should be viewed as an hereditary kingdom under Fairhair's sons and successors, Eric I of Norway and Haakon I of Norway. Some historians emphasize their inability to exercise actual monarchical control over the country and assert that St. Olav (Olaf II), who reigned from 1015, was the first king since Fairhair to control the entire country. Olav is traditionally held to be the driving force behind Norway's final conversion to Christianity. He was later also revered as "Rex Perpetuum Norvegiæ" (Latin: eternal king of Norway). Only under half-brothers Olav II and Harald III would succession begin to be determined by rules of inheritance, rather than the crown simply being taken by force.