An underlying theme of the film "El Cid" is the idea of Politics as Theater. The character Ben Yussuf (Herbert Lom) is the consummate stage actor. His every appearance and speech is dramatic. His costume is foreboding. His eyes flash. His arm points while his voice reverberates over the sands. His power comes from his acting ability.
(It's difficult to watch this character, his costume, the way he speaks and enters a scene, and not see him as a direct influence on George Lucas's Darth Vader. Lucas transported "El Cid"'s knights and conflicts to a new setting, sanitized them a bit to make them ahistorical and harmless, but it's the same kind of movie.)
Ben Yussuf's understanding of the nature of theater is shown when he unwraps a new actor-- the Spanish traitor he's about to insert into his enemies' midst. The scene is disturbing because it reminds us that politics and history can be stage-managed.
As Ben Yussuf plots, the knight Rodrigo adopts the role history and legend have ordained for him: The Cid. His career is made through public display. Like Yussuf, Rodrigo always seems to be declaiming before an audience, which by the end of the movie reaches the size of a large army. The strength of the Cid and his force comes from the part he plays.
(Charlton Heston, who plays Rodrigo, was always a tad theatrical, as if when he jumped to films early in his career he was unable to leave the stage behind. The huge 70mm screen was an appropriate venue for him. He's an able match for Lom's Ben Yussuf.)
The joust-- a tremendously thrilling sequence-- is Rodrigo's first major performance. He revels in it, shown by his dramatic words to the head of the rival Spanish camp afterward.
In due time, Rodrigo becomes the role. There's no escape from it.
The theater of politics is best shown at the end of the film.
With art, sometimes we're most affected by what we're not allowed to see.
The Cid is dying. Chimene, the King, and the Cid's lieutenants are in the room with him. Has he expired?
The camera turns off. The next shot is of his army in the morning, waiting silently at the gate for its leader.
What we're not shown is what's happened in the interim. Chimene and the others have had only a few hours before daylight to get the play ready-- to get the Cid clothed in his armor and placed atop his horse. As with a stage play, we don't see what took place backstage: the frantic activity of preparation. Our minds fill the gap.
The army waits-- then we're given a quick glimpse backstage, the costumers and dressers putting the finishing touches on the star performer.
He's led to the front, on his snorting, clip-clopping horse. King Alfonso, after kissing a cross, draws his sword and shouts encouragement to the other players. The gates open. (The curtain rises.) In a blaze of light: the Cid. On stage. One final appearance. He's seemingly overcome death itself.
Powerful, powerful, powerful.
Ben Yussuf is beaten by a better actor, or at least, by a better prop.