Full of resentment and fear, Marsile wants above all to have peace in Spain and to keep Saragossa away from the Franks. He hates Charlemagne bitterly for what he has done to Spain and wants revenge, but since he knows Charlemagne's kick-butt strength, he decides to use craftiness to augment his force. Deception is his most powerful weapon. As he admits to his council,
"I have no force that can break his.
Give me the counsel you owe me as my cunning vassals
And save me from death and shame!" (2.19-21)
Based on Blancandrin's plan, he deceives Charlemagne into leaving Spain and tricks the rearguard into a narrow mountain pass, where they are cut off from the rest of the army and overwhelmed by the Saracens' greater numbers.
But unlike many pagan knights, who are described as being just as courageous as the Frankish knights, Marsile is also cowardly. He flees when Roland cuts his hand off (142), in pathetic contrast to the Frankish knights who keep hacking at Saracens until they are headless"
King Marsile flees to Saragossa, […]
He lies down, a grisly sight, on the green grass.
He has lost his right hand completely,
He swoons and writhes with pain from the bleeding. (187.2570, 2573-75)
Don't get us wrong. In the Song of Roland, fainting and crying only enhance your manliness. Just take Charlemagne, who yields to no man in his love of weeping. Here's the difference: where Charlemagne cries in grief or anxiety, Marsile cries in pain. That's what makes him a coward. Real men fight to the death. Cowards flee.
Back in Saragossa he cowers in his room with his wife (women are another sign of weakness) and bemoans his fate while the virile Emir strides out to meet Charlemagne, promising even more revenge.
In the poet's black-and-white morality, all non-Christians are bad precisely because they are non-Christian. But Marsile's weakness gives him an extra layer of badness that sets him apart from Blancandrin, who swaggers into the Frankish camp, and the Emir, who fights Charlemagne in brutal hand-to-hand combat. Although his trickiness seems to come as a natural part of being pagan (if you can't rely on God's strength, you have to make your own work), Marsile's cowardice is all his own. To read more about how and why the Saracens are evil, see "Good v. Evil" under "Themes."