Ilium vs Ilion

Ilium and Ilion both are nouns.

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

As nouns, Ilium and Ilion are synonyms defined as:

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

Other synonyms of Ilium include Troy.

Ilium (noun)	Ilion (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