Orbital structure of in situ stellar halo. Top: stellar density distribution in R_max − Z_max coordinates for all in situ stars (first row) and kinematically defined (see Toomre diagram in Fig. 9) in situ stellar halo (second row). Bottom: distribution of the angles between R_max − Z_max as a function of the stellar age for all in situ stars (third row) and kinematically defined stellar halo (fourth row). The white vertical lines highlight five of the most significant mergers (M1–M5), in terms of the stellar mass ratio. Similar to a number of recent MW studies (see, e.g, Haywood et al. 2018; Koppelman et al. 2021) the HESTIA galaxies reveal a number of wedges in R_max − Z_max coordinates. The bottom rows show how these wedges emerge over time. We find that the individual structures in R_max − Z_max are made of stars predominantly made of stars that formed in between the significant merger events, suggesting a similar origin for similar structures in the MW.