Italian capital vs Eternal City

Italian capital and Eternal City both are nouns.

Word	Noun	Adjective	Verb	Adverb
Italian capital	Yes	No	No	No
Eternal City	Yes	No	No	No

As nouns, Italian capital and Eternal City are synonyms defined as:

Italian capital and Eternal City: capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire

Other synonyms of Italian capital include capital of Italy, Roma, Rome.

Italian capital (noun)	Eternal City (noun)
capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire	capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire