Gladiator makes this list for a number of reasons.
It is an epic movie, more like the spectacles of the 1950s than anything made recently. It uses CGI but only to create the world and frame the action in believable ways. From the opening battle scene to the Colosseum you find yourself looking at the details and immersed in the world.
The character played by Russell Crowe, Maximus, is not really a protagonist. He is the person we follow and we see much of the action from his perspective, but a protagonist is by definition changed by in the course of a story and Maximus does not change. He is himself right from the first battle and while he undergoes great changes in his situations, he remains himself.
Great ideas. Revealed in the course of the movie, it is the Roman ideal of Stoicism that Maximus portrays.
"What we do now echoes in eternity."
Here's the opening scene.