Catenary Arch is an arch assembled out of numbered blocks. The blocks are laid out on a horizontal board and then tilted into a vertical position. In spite of the fact that the blocks are relatively slender, they can stand due to their catenary shape. Visitors can compare the shape of the arch to the shape of a freely hanging chain and see that the shapes are the same. Graphics, drawings and photographs explain why the catenary is a good configuration for an arch. The mathematical formulae for the catenary are also presented.