Poem-of-the-Week: "Then we will fight in the shade"

A good line can last forever. (Well, for 2500 years, at least.) And it can appear in different media, in different languages, and in both classic literature and popular culture.

Here's a scene from pop culture that's hitting it big at the box office this month, with a famous 2500-year-old line at the end:



Here's another version of the very same scene from about 100 years ago, and even then it was “news that men have heard before”:

The King with half the East at heel is marched from lands of morning;
His fighters drink the rivers up, their shafts benight the air,
And he that stands will die for nought, and home there's no returning.

A prize can go to anyone who finds on the Library's shelves the next and final line of this verse, or identifies its author. (Or perhaps identifies "The King with half the East at heel.")