Could you please translate for us what etnikoi means? To my understanding Hellene means simply an ethnic group native to modern Greece including diaspora abroad, but Etnhic Hellene nowadays! means a follower of the ancient polytheistic Hellenic religion to extend reconstructed (Zeus, Hera, Apolon etc)Sorry, but no thing as Roman ethnicity existed. There was a Roman nationality, though, and multiple ethnic groups.
EDIT: By the way civitas means citizenship, not nationality. The former is a legal concept, whilst the latter is historically relatively new term intertwined with the ethnicity (present meaning).