Byzantium vs urban center

Byzantium and urban center both are nouns.

Word	Noun	Adjective	Verb	Adverb
Byzantium	Yes	No	No	No
urban center	Yes	No	No	No

Byzantium (noun)	urban center (noun)
an ancient city on the Bosporus founded by the Greeks; site of modern Istanbul; in 330 Constantine I rebuilt the city and called it Constantinople and made it his capital	a large and densely populated urban area; may include several independent administrative districts
a continuation of the Roman Empire in the Middle East after its division in 395