| 1766 | Euler proposed the rigidity conjecture. |
| 1813 | Cauchy showed that all convex polyhedral surfaces are rigid. |
| 1896 | Bricard showed that the only flexible octahedron had self intersections, so all embedded octahedra are rigid. |
| 1916 | Steinitz refined Cauchy's proof to show that a convex polyhedron was completely determined given its faces and a knowledge of which of their edges were joined. |
| 1974 | Gluck showed that "almost all" triangulated simply connected closed surfaces are rigid. |
| 1977 | Connelly found an embedded polyhedral surface that flexes as a counterexample for the rigidity conjecture. |
| 1981 | Roth refined Cauchy's proof of rigidity that a convex polyhedral framework is rigid iff every face of the polyhedron is a triangle. |
PREV: Introduction
NEXT: Rigidity Theories
Illustrated by Jonathan Shum
Center for Intelligent Machines
McGill University, Montreal, Canada.