Pergamon vs Pergamum

Pergamon and Pergamum both are nouns.

Word	Noun	Adjective	Verb	Adverb
Pergamon	Yes	No	No	No
Pergamum	Yes	No	No	No

As nouns, Pergamon and Pergamum are synonyms defined as:

Pergamon and Pergamum: an ancient Greek city located in the western part of what is now modern Turkey; the technique of preparing sheepskins as parchment was developed here

Pergamon (noun)	Pergamum (noun)
an ancient Greek city located in the western part of what is now modern Turkey; the technique of preparing sheepskins as parchment was developed here	an ancient Greek city located in the western part of what is now modern Turkey; the technique of preparing sheepskins as parchment was developed here