Clashes and raids on bordering Andalusian lands did not keep the Christian kingdoms from battling among themselves or allying with Muslim kings.[18] Some Muslim kings had Christian-born wives or mothers.[citation needed] Some Christian mercenaries, like El Cid, were contracted by taifa kings to fight against their neighbours.[18] Indeed, El Cid's first battle experience was gained fighting for a Muslim state against a Christian state.[citation needed] At the Battle of Graus in 1063, he a...