ATHENA is ESA next-generation large-class X-ray telescope, with a planned launch around 2030. The mission is designed to study the evolution of the hot-gas large structures and to understand how black holes grow and shape the Universe. In order to accomplish these tasks ATHENA will be equipped with the largest X-ray optics ever built. The calibration of the telescope is a critical aspect of the project and raises significant difficulties due to its unprecedented size and mass. The VERT-X project, financed by ESA and recently started at OAB, aims to design an innovative calibration facility based on an X-ray beam expanded and parallelized by means of an inverted X-ray collimator. In this seminar, after a short description of the ATHENA mission and the status of the calibrations of the present X-ray missions, I will discuss the main characteristics of the VERT-X project.