The author discusses the differential equation describing a catenary. The catenary can be generated by a power line hanging between two poles. In this paper some examples with respect to this curve are presented. Thus some geometrical examples are reviewed. For instance, the author considers the shape of the road for a square wheel with respect to a catenary. Furthermore, he describes the catenoid which is the corresponding surface of revolution. The catenoid is a minimal surface and the author shows that the area below it is not minimal.