With the name of "Menhirs", the sculptor once again shows his admiration for megalithic constructions. The study of the internal space of the previous series of Cubes opens the way to an investigation into the possibilities of the plane.

Mateos starts from a single initial plane which, after making a few cuts, he flexes and breaks to give rise to the three-dimensional form. This produces a rhythmic alternation of vertical volumes and spaces, which contrasts with the static nature of his previous work.

His research is framed within a rationalism in which form responds to a constructive logic. The sculptor is convinced that, just as nature has its laws, abstract art must respond to internal principles and logic. Mateos is developing his artistic thinking, which he will call "The Logic of Forms".

These Menhirs were the first result of an analytical investigation with the plane, which Mateos would develop recurrently throughout his career and which would mark his final stage.