I’m studying a poem by Margaret Junkin Preston and it’s called ‘A Bivouac In The Snow’. It’s about the American Civil War (The War Between The States).

In the poem it makes a reference to a ‘Xerxian army’.
Here is the whole stanza.

Round the bright blaze gather,
Heed not sleet or cold;
Ye are Spartan soldiers,
Stout and brave and bold.
Never Xerxian amy
Yet subdued a foe
Who asked but a blanket
On a bed of snow.

Does anyone know what the ‘Xerxian army’ is in reference to? I can’t seem to find it anywhere..

Any help, even just ideas or thoughts would be good.
Thanks