Method for constructing a tower of a wind energy generator

The present invention relates to a centering mandrel (50) for fastening to a first tower segment (16) of a concrete tower of a wind energy installation, and for guiding a second tower segment of the concrete tower when lowering the second tower segment onto the first tower segment. The centering mandrel comprises a fastening section (54) for fastening to the first tower segment and a guiding section (56) for guiding the second tower segment. Furthermore, the present invention relates to methods for erecting a tower of a wind energy installation.