Eternal City vs capital of Italy

Eternal City and capital of Italy both are nouns.

Word	Noun	Adjective	Verb	Adverb
Eternal City	Yes	No	No	No
capital of Italy	Yes	No	No	No

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

Eternal City and capital of Italy: 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 Eternal City include Italian capital, Roma, Rome.

Eternal City (noun)	capital of Italy (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