The catenary arch that we built
The red arch was built on a hinged building surface. Once the blocks were correctly positioned over an outline of the arch, we lifted the wooden platform to bring the blocks to a vertical position. Then we lowered the backboard, leaving the arch free-standing. The shape the arch takes is called a catenary. The catenary is the curve that an idealized hanging cable or chain with very short links assumes under its own weight when supported only at its ends.