Why is ローマ字 spelt without an ン?

Question

Why is ローマ字 spelt without an ン?

As far as I can tell, it's not because you can't have an ん sound before a じ sound, because 漢字 has an ん sound before 字.

Did early Europeans' term for Roman letters not use the letter "n"?

Also, does the ローマ in ローマ字 refer to the Roman empire whose language influenced the script used in many European languages, or did it refer to the main headquarters of the Roman Catholic Church, the religion of the Portuguese?

Background: I want to know the etymology for the word ローマ字 so that the next time someone misspells the English word romaji (derived from the Japanese word ローマ字) as "romanji", I can not only say that the English word should be spelt "romaji", but I can explain why it's spelt that way. And the more detailed and authoritative the explanation of "ローマ字"'s etymology is, the more likely it is to be remembered.

Answer 1

ローマ字 is ローマ plus 字, not Roman plus 字.

ローマ is a Japanese noun, derived from a noun (from Latin "Roma", meaning Rome), while Roman is an English adjective, derived from an adjective (from Latin "Romanus", meaning "of Rome, Roman").

Since ローマ字 does not come from the English word "Roman", it has no ン sound.

_{(Although ローマ is probably not directly from Latin, it doesn't appear to be certain which intermediate language(s) the word passed through. Wiktionary suggests that it was perhaps Spanish or Portuguese, but it doesn't list a source.)}