 In a dispute over the territory between the Cea and Pisuerga, Ferdinand, nominally a vassal of Bermudo III, defeated and killed his suzerain at the Battle of Tamarón on 4 September 1037.Ferdinand took possession of León by right of his wife, and on 22 June 1038 had himself crowned and anointed king in León.On 15 September 1054, Ferdinand defeated his elder brother García at the Battle of Atapuerca and reduced Navarre to a vassal state under his late brother's young son, Sancho García IV.