Why did the poet change the people and events? What message and purpose do the changes support?

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, and indeed the poem has been characterized by some scholars as "propaganda" to encourage Christians to take up arms against Islam. "Propaganda" here is a loose term, including a broad range of artistic creations that can intend to push listeners to action or simply paint certain policies or events from a specific perspective.

Those familiar with the events of the poem will notice several divergences between the poem and history. For one thing, the adversaries of the poem are Saracens (called also in the poem "pagans"), not Basque natives. And while Einhard's account mentions Roland, the other chief characters of the poem are missing. As a result, the Song of Roland more or less ignores this history, depicting instead a Charlemagne capable of conquering all of Spain. The account is legend. Roland, instead of being "Lord of the Breton March," as detailed by Einhard, is a Frankish lord and Charlemagne's own nephew. The "treachery" of the Christian Basques becomes transformed into the treachery of a single man, Ganelon, and the Basques themselves are replaced by Moslems, whom the poet calls Saracens or pagans. The battles are epic and grand, worthy of intervention by God himself, and historical ambiguities or defeats are ignored.