No! Persia's matchless millionsNo human power can quell, Such native valour arms her sons,Such might incomparable!
This section here shows how highly the Persians think of themselves. It equates them to being incomparable, as having no equal in military might. This is quite interesting considering they have been defeated by the same foe only a few years prior at the battle of Marathon, thus the Persians clearly have equals, or perhaps even superiors in these terms. They do have more numbers than they had on their previous march to fight the Athenians, Spartans, etc. than when they lost at Marathon. It's similar in irony to the Titanic being an "unsinkable" ship, only to sink on its maiden voyage. Here the Persians are saying the same thing, that they are incomparable in strength, and yet we find out later that they are in fact not incomparable.
Zach Long CC BY-NC-ND