On Charlemagne Crossing the Pyrenees to Attack the Moors In 778, Getting Defeated Decisively at Saragossa, and Afterwards While Heading Back to His Kingdom Getting Ambushed by Basques Forces at Roncevaux Pass Losing a Sizable Portion of His Army

Yeah, 778 was clearly not Charlemagne's best year, to say the least (though, yes, the Franks gradually did make progress in Northern Spain when Charlemagne's son, Louis the Pious, was put in charge of that particular campaign; seizing some land and making the Moors sweat a bit).