Viggo would make a great Achilles. But he's too old to play Alex, who died at about 30, with most of his story taking place in his early 20s.
Viggo would make a good Achilles. I think his role in Fellowship of the Rings shows that he truly gets how to play a conflicted hero. Hollywood usually does it with lazy short hand, but I thought that Viggo Mortenson really got it with some nuanced acting that was just wonderful in the theatrical version of FOTR. It shows up even more in the extended DVD version.
A phrase I never want to hear in my life though is... "Keanu Reeves is Julius Caesar-- Coming to a theater near you"