The vertex of a tetractys denotes the mathematical point. The pair of dots denotes the endpoints of a straight line. The three dots denote the three vertices of a triangle and the four dots in the last row of the tetractys denote the four vertices of a tetrahedron, the simplest regular polyhedron. The tetractys therefore symbolizes the mathematical sequence of a point, line, triangle & tetrahedron. They are the basic building blocks of geometry in spaces with, respectively, zero, one, two & three dimensions.