This article seeks to provide a close reading of Yannis Ritsos’ “Ajax” (Fourth Dimension), a poem that heretofore has not received adequate scholarly attention. On a first level, emphasis is laid upon the monologue’s thematic and verbal affinities with Sophocles’ Ajax, in an attempt to highlight Ritsos’ knowledgeable relationship with the ancient text. In spite of the similarities shared by the two poems, however, Ritsos’ Ajax diverges from his sophoclean counterpart on several points, adopting a stance that is imbued with an existentialist hue. Accordingly, on a second level the study attempts to approach Ritsos’ poem through the scope of existentialism, drawing links with the philosophical and literary/theatrical work of French Existentialists in general, and Jean-Paul Sartre in particular. The article falls into two sections. The first section embarks upon an analysis of Ritsos’ “Ajax” as a whole. The second section focuses attention on a particular feature of the poem - the black ‘fly’ that ‘troubles’ Ajax throughout his monologue. As I propose, the function of the fly becomes clearer if examined in conjunction with Sartre’s play “The Flies”.