more than 10 Gyr of evolution with this technique, while in previous cluster simulations only a small time span, from $z=0.5$ onwards, could be covered ([@2005MNRAS.364..607M]). In this paper we present the first replacement simulation carried out for a MW sized halo, using the ErisDARK cosmological simulation carried out in the concordance $\Lambda$CDM model ([@2013ApJ...765...10K]; [@2014ApJ...784..161P]). The simulations are carried out with state-of-the-art massively parallel N-Body codes, PKDGRAV2 ([@2001PhDT........21S]) and ChaNGa ([@changa2008]; [@changa2010]; [@2015ComAC...2....1M]; http://www-hpcc.astro.washington.edu/tools/changa.html) on the CRAYXE6 “Monte Rosa” of the Swiss National Supercomputing Centre.

The paper continues with Section 2 where the replacement technique and numerical simulations are presented in details. Next the analysis methods and results are enumerated in Section 3. Section 4 contains an extensive discussion regarding the implications of the results for the origin of dSphs, including their relation to observational data. Finally Section 5 includes the conclusion and outlook of the presented work.

Numerical simulations and replacement technique {#sec2}
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Initial conditions and selection procedure
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The initial conditions of the simulations of this paper are based on the ErisDark run ([@2014ApJ...784..161P]), which is a dark matter only cosmological gravity run of 40 million particles using the $\Lambda$CDM cosmological model ($H_0$ = 73 km 