Eagle -- Semi-sacred standard of a legion; symbol of Roman power

Great southern king -- Augustus

Karl -- Warrior

Skald -- Bard

Southern men -- Romans

The battle -- Teutoburgerwald [1] in 9 CE in which Hermann (Arminius) and the Cherusci with allied tribes defeated Legiones XVII, XVIII, and XIX under Publius Quinctilius Varus during a great storm in the forest of Teutoburg

Thrall -- Slave

Thunderer -- Thor/Donar

Thusnelda -- Daughter of Segestes of the Cherusci

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[1] An excellent article on Teutoburgerwald by Jona Lendering may be found at Livius. See also Fifteen Decisive Battles of the World by the exuberant Victorian Edward Creasy.