On the afternoon of August 15, 778, the rear guard of Charlemagne's army was massacred at Roncesvals, in the mountains between France and Spain. Einhard, Charlemagne's contemporary biographer, sets forth the incident as follows in his Life of Charlemagne:
While the war with the Saxons was being fought incessantly and almost continuously, [Charlemagne] stationed garrisons at suitable places along the frontier and attacked Spain with the largest military force he could muster; he crossed the Pyrenees, accepted the surrender of all the towns and fortresses he attacked, and returned with his army safe and sound, except that he experienced a minor setback caused by Gascon treachery on returning through the passes of the Pyrenees. For while his army was stretched out in a long column, as the terrain and the narrow defiles dictated, the Gascons set an ambush above them on the mountaintops—an ideal spot for an ambush, due to the dense woods throughout the area—and rushing down into the valley, fell upon the end of the baggage train and the rear guard who served as protection for those in advance, and in the ensuing battle killed them to the last man, then seized the baggage, and under the cover of night, which was already falling, dispersed as quickly as possible. The Gascons were aided in this feat by the lightness of their armor and by the lay of the land where the action took place, whereas the Franks were hindered greatly by their heavy armor and the terrain. In this battle Eggihard, the surveyor of the royal table; Anselm, the count of the palace; and Roland, prefect of the Breton Marches, were killed, together with many others. Nor could revenge be taken at the moment, for as soon as the act had been done, the enemy scattered so completely that no trace of them was left behind.
To make sense of his excursions into Spain, we must know that Charlemagne (742?-814), king of the Franks, was a committed, militant Christian. A loyal ally of the pope and a great