what was the contribution/s of Charlemagne?

The poem describes events happening several centuries earlier, during the reign of the mighty Christian warrior-king Charlemagne. The historical context of the poem therefore straddles several centuries, and to properly understand the poem we must bear in mind its rich historical background.

The poem is a legendary account with some basis in reality: in 778, the rearguard of Charlemagne's army was slaughtered in the Roncesvalles (old French: Rencesvals) pass of the Pyrenees mountains. Accounts from this dark period of European history are always problematic, but the most reliable European account of the event comes from Einhard, Charlemagne's own biographer:

At a moment when Charlemagne's army was stretched out in a long column of march, as the nature of the local defiles forced it to be, these Basques [Wascones], who had set their ambush on the very top of one of the mountains, came rushing down on the last part of the baggage train and the troops who were marching in support of the rearguard and so protecting the army which had gone on ahead. The Basques forced them down into the valley beneath, joined battle with them and killed them to the last man. They then snatched up the baggage, and, protected as they were by the cover of darkness, which was just beginning to fall, scattered in all directions without losing a moment. In this feat the Basques were helped by the lightness of their arms and by the nature of the terrain in which the battle was fought. On the other hand, the heavy nature of their own equipment and the unevenness of the ground completely hampered the Franks in their resistance to the Basques.