The argument to \chapter is supposed to be the title of the chapter. If your chapters have no title, leave that blank.
Use
for a chapter without a number.
The word used in the title of the chapters is stored in a command called "\chaptername". You can change this like so:
Code:
\renewcommand{\chaptername}{LIBER}
The numbering of the chapters is taken care of for you. You shouldn't need to insert them yourself. If you want them to show up with Roman numerals rather than arabic numerals, however, you should put it:
Code:
\renewcommand{\thechapter}{\Roman{chapter}}
Both can go in your preamble.
In the document is in Latin, you should load the hyphenation patterns for Latin. I'll check to see if I can figure out how this is done.
EDIT: It's
Code:
\usepackage[latin]{babel}
You might want to consult the Documentation for
babel having to do with Latin for some additional Latin-specific options.
(BTW, this changes the name of the chapters to "Caput", but you can still change it to LIBER as described above; just do that after loading babel.)
Consider adding:
right after \begin{document}. With a small page, LaTeX is rather too fussy and ends up running things into margins rather than putting larger gaps between words on a given line.
There are some other funny things about your code. The packages:
Code:
\usepackage{fontspec}
\usepackage{xunicode}
\usepackage{xltxtra}
Are meant for use with XeLaTeX, which is geared to use true type and open type fonts. Yet nowhere do you load any such fonts. And right after that you have:
Code:
\usepackage[T1]{fontenc}
That's basically telling it to use Type 1 fonts, typically used with regular LaTeX or pdfLaTeX. Which is it? Pick one and stick with it.
Feel free to visit us at the forums at
latex-community.org for more help. I'm on there a lot, as are many who know more than I.