The Gaia DR2 has permitted to understand that the major part of what was thought to be the in-situ Galactic halo of the Milky Way is in fact the remnant of one important merger that probably occurred more than 9 Gyr
ago. These results have opened new interesting questions : what are the characteristics of this accretion event ? Where is the in-situ Galactic halo ? How is it connected to the Galactic thick disk ? We will present these results and discuss the new perspective about the old stellar populations of our Galaxy.