The role that accretion events have played in the evolution of the Milky Way, as well as the quest for finding the possible remnants that are at the origin of the old disc, have been a central topic in Galactic archaeology for more than five decades. The advent of the European space mission Gaia have enabled us to measure much more accurately the positions and the 3-dimensional velocities of millions of stars in a volume several kiloparsecs wide, shedding unprecedented light on the above mentioned questions.
On the one hand the discovery of ripples in the Galactic disc, have illustrated that its morphology and characteristics, at all radii, continue being impacted by external factors. On the other hand, the discovery of kinematic groups outside the disc, such as Gaia-Enceladus, Sequoia or Thamnos are all believed to be remnants of past accretions, but it is still unclear whether they are distinct features or not, nor to what extent they could have contributed at the origin of the thick disc and/or the inner halo.
Retrograde stars in the Milky Way hold, in that respect, a key place in our understanding of the assembly history of our Galaxy because there is no clear mechanism that could form them exclusively in situ. In this talk I will review the recent results on this topic, based in particular on 3d kinematics and abundances of stars in the extended solar neighbourhood.