The 1963 Cinerama Dome was built from precast concrete hexagons and pentagons. The fourth basic shape is the polygon, including pentagons and octagons. The tessellation uses three types of tile, an equilateral triangle and two irregular pentagons. Such shapes are called polygons and include triangles, squares, and pentagons. The sides of a regular dodecahedron are regular pentagons, which for Pythagoreans symbolized health. Figurate numbers representing pentagons (including five) are called pentagonal numbers. Each hexagon is divided into four pentagons. The stellated pentagons have sides intersected by others. For example, a regular hexagon bisects into two type 1 pentagons. The other pentagons of the figure do not have inscribed pentagrams. As the internal angle increases for squares, pentagons and so forth, the stability decreases. The pentagram map is the identity on the moduli space of pentagons. There are many tiling topologies that contain type 1 pentagons. This detailed procedure involving Carlyle circles for the construction of regular pentagons is given below. There exist cyclic pentagons with rational sides and rational area; these are called Robbins pentagons.