A Goliath (gantry) crane is similar to a top running crane except that the crane bridge is supported by legs and the rails are at ground level. The additional leg structure makes the crane more expensive, this is offset by the considerably cheaper low level rails. That advantage increases with increased track length making them particularly suitable for large outdoor stockyards. There is an additional safety hazard arising from travelling on low level rails which must be considered, but this can usually be taken care of easily and ground level rails can be advantageous compared to the obstruction caused by the building structure columns. They can be of single or double girder design with similar construction methods. Furthermore they can be designed with a cantilever at one or both ends.