Ilion vs Ilium

Ilion and Ilium both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ilion	Yes	No	No	No
Ilium	Yes	No	No	No

As nouns, Ilion and Ilium are synonyms defined as:

Ilion and Ilium: an ancient city in Asia Minor that was the site of the Trojan War

Other synonyms of Ilion include Troy.

Ilion (noun)	Ilium (noun)
an ancient city in Asia Minor that was the site of the Trojan War	an ancient city in Asia Minor that was the site of the Trojan War