Abstract: A mobile crane has main and auxiliary counterweight assemblies and is arranged such that the spar or mast on which the auxiliary counterweight assembly is mounted is of a two-piece construction such that, upon the imposition of a load on the main boom of the crane which is sufficient to deflect the boom, the outer end or tip of the spar pivots to lift the auxiliary counterweight assembly from the ground, thereby opposing the bending forces imposed on the boom and allowing the platform to rotate about a vertical slewing axis without obstruction from the auxiliary counterweight assembly. The spar and thus the entire crane is compact, lightweight, easy to assemble and disassemble, and can operate in a relatively restricted space without interference from obstacles around its rear.