We analyze a corpus of historical texts in terms of complex network theory. This is done by means of the Patrologia Latina, a collection of Latin documents that were written over a period of more than 1,000 years. We perform a lemmatization of this corpus and map its documents onto the end of the productive period of the corresponding authors. By means of this temporal ordering, we perform a transitivity analysis on the level of lexemes and sentences as a function of time. This analysis shows a remarkable law-like behavior of transitivity on the lexical and sentential level.