Oh look, it's also likely the same noble who captured the dwarf king too, for extra value in revenge and less sympathy for whatever's about to befall him.
@quagzlor - I think it's more like @AdamKnight said.
500 Soldiers (some OP by themselves), and a city wall filled with as many riflemen as they can have barrels (and ammo, and bullets) for.
A lot of drilling is needed for the militia to become a solid force on a battlefield, but for shooting from a wall just a day or two should be enough. (Plus the morale penalty for the attackers, when the defenders apparently "have hundreds of magic-users".)
What is the point of having wars when a single meteor strike can decimate the entirety of the human army? How did humanity even survive this long? I guess strong human characters are going to be introduced.