In the style which I'm sort of copying, dates are printed against the left margin and the entry's heading (which doesn't need to conform to LaTeX sectioning commands) is centered.
I have borrowed code from another answer but it didn't produce what I expected; the centered text is missing (I admit that manipulating this is a bit outside of my wheelhouse.) I don't think that the centering group or center environment are what I want (centering would be it if I didn't need the date to be to the left just inside the margin.
\documentclass[11pt]{article} \usepackage{showframe} \usepackage{makecell} \newlength{\LeftItem} \newlength{\CenterItem} \newcommand{\entry}[2]{% \par \settowidth{\LeftItem}{ #1}% \settowidth{\CenterItem}{\Large #2}% \noindent \makebox[0pt][l]{\ #1}\hfill \makebox[0pt]{% \ifdim\LeftItem>.5\dimexpr\linewidth-\CenterItem\relax \makecell[t]{\strut \\ #2}% \else \par }% } \begin{document} \entry{25.}{S. Gulielmi Abbatis.} \end{document} 
