How are Muslims portrayed in The Song of Roland?
The portrayal of Muslims in The Song of Roland tells us absolutely nothing about medieval Muslims, but it tells us a great deal about medieval Christians and the world-view of the Crusaders in particular. The Saracens (this was the medieval European term for Arabs, and, by extension, all Muslims) are portrayed as the mirror-image of the Christians—both the same and reversed. Their society is identical to Christendom in form, but opposite in content. For instance, the Saracens of The Song of Roland worship a trinity—formally, this is identical to Christian practice—but this trinity is composed of Mohammed, Termagant, and Apollo. Medieval Christians did not understand that Muslims respect Mohammed as a prophet, but emphatically do not worship him as a god. Termagant was an overbearing female deity having absolutely no existence outside of medieval Christian perceptions of Islam. Apollo is the ancient Greek god of poetry and music; nowhere but in The Song of Roland are Muslims said to worship him. It seems that he is included in the Muslim trinity here for his general odor of archaic paganism. So we see here that while the Saracens have a sort of trinity, it is composed of figures that medieval Christians would see as nothing but nasty and ridiculous little idols. And because their arrangement and invocation mirror that of the Christian trinity, they have a distinct air of blasphemy. This combination of formal similarity to Christian practice and complete reversal in terms of content is an operation that the poet uses consistently to describe the Saracens; we see it again in the twelve evil and treacherous barons selected by Marsilla to fight the twelve noble peers of France (the association between the twelve latter peers and the Apostles again adds an implicit blasphemous touch to the Islamic arrangement), Baligant's imitation of Charlemagne in his selection of a name for his sword, the boasts the Saracens make of going to Aix someday to force Charlemagne to convert to their religion in a sort of counter-Crusade, and so forth. Essentially, Islam is presented as Christianity's evil twin.
Compare and contrast Roland and Olivier.
As the poet puts it, "Roland is bold, Olivier is wise, / and both of them are marvelously brave" (87.1093-1094). The companionship of Roland and Olivier is an opportunity for both to be shown to be heroically tender; even more importantly, Olivier is the perfect foil for Roland, sharing all his qualities of valor and vassalage but differing from him in the most interesting, most troublesome aspect of Roland's character—his boldness—and thus setting off this quality of Roland's by contrast. Roland's boldness causes him to make his great mistake at Roncesvals—he is too proud to call for help from Charlemagne, refusing to blow his oliphant when Olivier urges him to, and the men he commands end up, arguably, losing their lives almost as much to Roland's outrageous vanity (as Olivier says, "Those French are dead because of your caprice," (131.1726)) as to Ganelon's treachery. The Franks were, as Olivier puts it to Roland, "doomed to see your prowess"; they get a splendid show of Roland's valor and courage, but, faced with an absolutely overwhelming Saracen force and no real shot at victory, every single Frank dies (131.1731). But the glory of Roland's death—neither Olivier nor any of the rest of Roland's comrades get such a splendid reception as he does from the heavenly hosts—and the linking of events that takes us from the slaughter at Roncesvals to Charlemagne's triumph over Baligant and taking of Saragossa lead us to consider what it is that makes Roland's folly even greater and worthier than Olivier's prudence in the eyes of the poet.
What techniques does the poet use to unify the many events of The Song of Roland into a whole?
The Song of Roland is organized on every level around repetition—from the joining of the lines of each laisse through assonance (the repetition of the final vowel sound of each line) to the recurring phrases to the laisses similaires—and symmetry—from the combat of Charlemagne and Baligant, which resembles that of warring reflections divided by a mirror, to the overall bilateral symmetry of the plot.