And Argonia is...? Capital of Black Marsh? (Random guess)
It′s another name for Black Marsh, the meric one.
On topic: Their strength was not their numbers, but that they were without fear (atleast the scamps) and that they′d return after deafeat. Again and again and...
The Argonians were frenzied and the Daedra were sent into the Darkness, only to return and face the frenzied Argonians and be sent into the Darkness and...
That′s why they closed the gates to Black Marsh.
EDIT: ninja`d