This article aims to analyze the use of the Middle Ages as a reference for Catholic fundamentalism in the 21st century. To this end, we have divided it into three parts. First, we present the emergence of fundamentalism in the early 20th century in the Protestant context of the USA. At the same time, we have noticed that there are several points of contact between Protestant and Catholic fundamentalism, especially when both criticize the worldview proposed by Enlightenment philosophers. Having identified the main features of fundamentalism in the 20th century, in the second part of this article we will analyze Catholic fundamentalism, taking into account some conservative Catholic organizations that were founded at that time. In the third part, we analyzed the group Arautos do Evangelho (Heralds of the Gospel) and the way they use the Middle Ages to build and legitimize a discourse against modernity and the ideas of social equality, since for them inequality should be a guiding principle, as it was in the Middle Ages.