Pergamum vs Pergamon

Pergamum and Pergamon both are nouns.

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

As nouns, Pergamum and Pergamon are synonyms defined as:

Pergamum and Pergamon: 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

Pergamum (noun)	Pergamon (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