Roman vs Eternal City

Roman and Eternal City both are nouns.

Word	Noun	Adjective	Verb	Adverb
Roman	Yes	Yes	No	No
Eternal City	Yes	No	No	No

Roman (noun)	Eternal City (noun)
a resident of modern Rome	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
an inhabitant of the ancient Roman Empire

Roman (adjective)	Eternal City (adjective)
of or relating to or supporting Romanism
of or relating to or derived from Rome (especially ancient Rome)
characteristic of the modern type that most directly represents the type used in ancient Roman inscriptions