Roncevalles (Ronceveaux in French) is famous for the Battle of Roncevalles Pass - especially for the rather embellished and distorted legend it became, as recounted in the Song of Roland (La Chanson de Roland), the oldest work in French literature.
On 15 August 778 Charlemagne (742/747-814), King of the Franks, was returning to his Frankish kingdom over the Pyrenees from Spain, when the rearguard of his army was opportunistically attacked, slaughtered and robbed at Roncesvalles Pass by native Basques. This was the worst defeat of Charlemagne's reign. Among these unfortunate soldiers was a certain Hrodland, Prefect of the Breton Marches.
However the epic chronicler of the Song of Roland has airbrushed history somewhat in order to retrieve Frankish pride and to accord with a growing sense of Frankish Christian national identity. Hrodland has turned into Roland, Charlemagne's nephew; the Basques have become the Saracens; and this time Charlemagne heads back to Spain to avenge the death of his knights.
In the Chanson 400,000 infidel Saracens ambush the small band left behind to guard the pass. Roland, with his trusty sword, Durandal, and his men fight heroically but are impossibly outnumbered. Charlemagne has told Roland to summon him back if in trouble by blowing his horn. This Roland refrains from doing until only a few of his brave knights remain alive. When he does finally put the horn to his lips birds fall from the trees, the ground shakes, chimneys topple down from houses, and people cry out from the pain in their ears. Charlemagne turns back but it's too late for all have perished.
The Song of Roland exists in various different manuscript sources, the earliest version being the Oxford manuscript dated somewhere between 1140 and 1170. It's an example of a chanson de geste, a literary form of epic poetry telling heroic deeds, written between the 11th and 15th centuries. Lines of early chansons de geste have assonantal endings, but later poems are fully rhymed.
Charlemagne is a pivotal figure in European history. He's considered the founding father of France and Germany. Indeed he was instrumental in christianizing and unifying the whole of Europe. He turned the Frankish kingdom into a Frankish empire, and, having conquered Italy, was crowned Emperor by the Pope.