two rivers: Tigris and Euphrates.
champaign with less rivers: Open country (Mesopotamia) with tributaries.
glebe: Soil.
Araxes: Aras, a river flowing through Armenia into the Caspian Sea.
drouth: Desert.
Ninus: Eponymous founder of Nineveh and King of Assyria.
Salmanassar: Assyrian king who led the ten tribes of Israel into captivity in 726 bc.
wonder of all tongues: A pun. Babylon was often identified with Babel.
him: Nebuchadnezzar, Babylonian king who conquered Jerusalem.
Cyrus: Founder of the Persian Empire. He conquered Babylon in 538 bc and freed the Jews.
Hecatompylos: The Parthian capital (Greek, ‘hundred gates’).
Emathian: Macedonian.
Ctesiphon: The winter capital of the Parthian kings.
dread in flight: Parthian mounted archers would shoot to the rear while feigning retreat.
endorsed: Carrying on their backs.
Agrican: Tartar king who leads an army of 2,200,000 in Boiardo’s Orlando Innamorato.
prowest: Most valiant.
paynim: Pagan.
engage: (1) Exhort; (2) ensnare. The double negative (not … on no) admits a Satanic ambiguity as to how much protection Satan is really offering.
opposite: Opposing, resisting.
Maugre: Despite.