Rostov on Don vs metropolis

Rostov on Don and metropolis both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rostov on Don	Yes	No	No	No
metropolis	Yes	No	No	No

Rostov on Don (noun)	metropolis (noun)
a seaport on the Don River near the Sea of Azov in the European part of Russia	people living in a large densely populated municipality
	a large and densely populated urban area; may include several independent administrative districts