 When the narrator describes the Persian confusion with the troops at  the rear wishing to advance and those in the front line wishing to  retreat, he uses lines from the poem "Horatius" by Thomas Babington  Macaulay, written in the 19th Century about a small Roman force  which held a narrow bridge against a much larger army. From the  poem: "Was none who would be foremost to lead such dire attack: But  those behind cried Forward!, and those before cried Back!"