Deposited in DRO : 08 March 2018 Version of attached le : Accepted Version Peer-review status of attached

We study the incidence of group and filamentary dwarf galaxy a ccretion into Milky Way (MW) mass haloes using two types of hydrodynamical simulations: EAGLE, which resolves a large cosmological volume, and the AURIGA suite, which are very high resolution zoom-in simulations o f individual MW-sized haloes. The present-day 11 most massive satellites are predominantly ( 75%) accreted in single events, 14% in pairs and 6% in triplets, with higher group multiplicities being unlike ly. Group accretion becomes more common for fainter satellites, with60% of the top 50 satellites accreted singly, 12% in pairs, and28% in richer groups. A group similar in stellar mass to the Large Magellanic Cloud ( LMC) would bring on average 15 members with stellar mass larger than 10 M⊙. Half of the top 11 satellites are accreted along the two rich est filaments. The accretion of dwarf galaxies is highly anisotropic, taki ng place preferentially perpendicular to the halo minor axis, and, within this plane, preferentially along th e alo major axis. The satellite entry points tend to be aligned with the present-day central galaxy disc and sa tellite plane, but to a lesser extent than with the halo shape. Dwarfs accreted in groups or along the riches t filament have entry points that show an even larger degree of alignment with the host halo than the full sa tellite population. We also find that having most satellites accreted as a single group or along a single filame nt is unlikely to explain the MW disc of satellites.