In a hierarchical galaxy formation scenario a massive spiral galaxy, like the Milky Way is the result of many merging events. Some of the stars that formed in the accreted galaxies must retain a very high kinetic energy and display space velocities and orbits very different from those of disc stars, like the Sun. The exquisite astrometry of the Gaia mission allows us to select stars with extreme velocities, some of which are likely witnesses of ancient accretion events. We present the preliminary results of a FORS/VLT spectroscopic campaign devoted to the characterization of a sample of these extreme velocity stars. As expected, our stars are moderately metal-poor and mostly on halo-like orbits. Stars associated with the Gaia-Sausage-Enceladus accretion event are a prominent group in our sample (26%). Our sample also includes a group of stars in retrograde motion confined to the Bulge region, a group of apparently young or evolved blue straggler stars and a likely unbound star.
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