This could -

Be big. This crane is so large, it has to travel on the road with no jib. The blue piece on top is the main jib A frame. It has tie bars to the jib, when it is fitted, and the winch wires raise the jib and A frame together. The A frame can be pushed over, to the front, by the hydraulic cylinders holding it up now. It then becomes a temporary jib to allow the crane to lift components and build itself. For speed, the assembly is often done using a second, smaller, crane.