A method and a device for assembling a structure that is formed from several modules that are disposed on top of each other, e.g. a wind power plant. An auxiliary mast of modular construction is erected parallel to and laterally of the structure to be erected, wherein the length of an auxiliary mast module approximately corresponds to the length of a structural module. A respective auxiliary mast module is previously detachably connected to a respective structural module to form an overall module, such that the auxiliary mast module can accept the weight of the structural module. The overall modules that are each formed from one auxiliary mast module and one structural module are moved by means of the lifting gondola in an upward direction along the auxiliary mast of previously erected structural modules to the level of the assembly position.