Francesc Eiximenis (c. 1330–1409), one of the most prominent Catalan authors of the late Middle Ages, remains little known abroad. The aim of this article is to present Eiximenis as an expert, at least to some extent, in the field of military affairs, using selected fragments of Dotzè llibre del Crestià, in which he discusses issues related to warfare. Eiximenis' unfinished encyclopedia, is undoubtedly his most important work of the Catalan Franciscan. It is also the least studied text of Eiximenis, as only the Twelfth volume has seen a contemporary, albeit still incomplete, edition. Eiximenis' reflections on the education of soldiers are found in the Twelfth Book. The Treatise on Military Affairs is educational and practical as the author's aim was not to create an erudite compilation, but rather a simple compendium or manual for city councils and feudal lords. The practical nature dominates the text over philological rigor, and the sources cited by the author do not always contain the attributed content or sometimes do not exist at all.