At the beginning of The Song of Roland, the Saracen King Marsile is losing his war against the Emperor Charlemagne. Only the city of Saragossa is left standing in the face of the Frankish onslaught. Blancandrin, the wisest of his counsellors, suggests that the king should send messengers to Charlemagne to sue for peace. Marsile, who is a Muslim, will convert to Christianity, declare himself the vassal of Charlemagne, and give up much of his treasure if the Franks will leave Spain and return to Aix.
King Marsile, then, sent a message with the express intention of making peace, an aim which would have been achieved if Charlemagne had not made the mistake of sending with his (positive) reply the treacherous Ganelon, who promptly betrayed the Franks to the Saracens, leading to the main action of the poem in the Battle of Roncevaux Pass.