Rules for the use of roman numerals in portuguese

Question

I know that commonly, the roman numerals are used to refer to a date or, more precisely, to a specific century, like in the examples below:

• Aconteceu no século XX;
• Um dos livros mais importantes do século XVIII;

I'd like to know if there is some rule to use this type of number in portuguese. Should they just be used to talk about a century or is this just a convention?

Can I use it to say something like "Eu tenho X anos" or not?

Answer 1

I'd like to know if there is some rule to use this type of number in portuguese. They are only allowed to talk about a century or this is just a convention?

Yes, there's a rule. Usually, roman numerals are used for:

• Centuries;
• King/Pope Names;
• Parts of a book or written piece, like a play script;

Additionally, the spoken rule is:

• Until the tenth numeral, is an ordinal numeral:

  No capítulo II (capítulo segundo), estudamos fonema e letra.

• After the tenth numeral, is a cardinal numeral:

  O volume XII (volume doze) desta coleção traz biografias de pintores.

Exception: if numeral comes before the substantive, is spoken always as an ordinal number:

O XI capítulo (décimo primeiro capítulo) pareceu-me mais longo.

Can I use it to talk something like Eu tenho X anos. Or not?

No, for this case it is wrong.

Answer 2

No.

See this link:

It should be used to refer to

• Centuries, like "As grandes navegações ocorreram nos séculos XV e XVI."
• Book or films chapters, volumes, parts or some other division, like "Veja mais informações no Capítulo V." or "Episódio VI: O retorno de Jedi".
• Popes, kings and emperor names, like "O papa Bento XVI renunciou.", or "O imperador Dom Pedro II governou o Brasil por 49 anos."