The main aim of this essay is to give a coherent and comprehensive interpretation of all the sources in which irrational feet are mentioned. The subject is analysed with a specific rhythmic point of view, taking into account the problems connected with the performance of ancient poetry and music. Such an approach gives a contribution and a new perspective for the solution of the problems left open within this topic. The texts are taken from the treatises written by Aristoxenus, Aristides Quintilianus, and Hephaestion. A specific chapter is devoted to the famous and debated statements made on this issue by Dionysius of Halicanassus in De compositione verborum.