How to type roman numerals?

Not sure what you mean by "lines," but you can find special Roman Numeral characters in the Character Palette (Edit > Special Characters), View = Code Tables, Tab = Unicode, Row = 00002150 Number Forms, 2160 and up.

I found what you suggested, but these are (or at least very much seem to be) the same characters like just typing the letters (VI, X, etc).

The difference is that the number forms are single characters. Ⅷ is one character and not 4 , like VIII.

What I meant with lines is something like this: http://www.lernumgebung.ch/Mittelstufe%2056/56uebungen/56muu/5MU026/romannumbers .jpg

I don't see any font on my system which includes lines like that in the number form characters, and I don't think there is any way to add them to the Latin version. To get the lines you would probably need to make a custom number forms font or do it via graphics.

Bjorn and Tom, some history, notably the second paragraph;

http://en.wikipedia.org/wiki/Romannumerals#Alternateforms

Thanks for that interesting link! If you use the combining overline (U+305) and underline (U+332) characters you can get something like this: V̲̅I̲̅I̲̅I̲̅ But I think having the letters connected looks a lot better.

I googled, but haven't found anything fitting. Any ideas where I should look?

Google seems like the only possibility. Something like this?

http://www.caltabiano.net/shareware/sicilian_numerals.html

Have a look at this:

http://www.dml.indiana.edu/use/mac/annotate.html

Scroll about 2/3 the way down.

According to

http://en.wikipedia.org/wiki/Roman_numerals

Roman numerals do not have a line above and below.