Rostov na Donu vs Rostov on Don

Rostov na Donu and Rostov on Don both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rostov na Donu	Yes	No	No	No
Rostov on Don	Yes	No	No	No

As nouns, Rostov na Donu and Rostov on Don are synonyms defined as:

Rostov na Donu and Rostov on Don: a seaport on the Don River near the Sea of Azov in the European part of Russia

Other synonyms of Rostov na Donu include Rostov-on-Don, Rostov.

Rostov na Donu (noun)	Rostov on Don (noun)
a seaport on the Don River near the Sea of Azov in the European part of Russia	a seaport on the Don River near the Sea of Azov in the European part of Russia