  We present a study of the role played by realistic three-body forces in
providing a reliable monopole component of the effective shell-model
Hamiltonian. To this end, starting from a nuclear potential built up within the
chiral perturbation theory, we derive effective shell-model Hamiltonians with
and without the contribution of the three-body potential and compare the
results of shell-model calculations with a set of observables that evidence
shell-evolution properties. The testing ground of our investigation are nuclei
belonging to fp shell, since the shell evolution towards shell closures in 48Ca
and 56Ni provides a paradigm for shell-model Hamiltonians. Our analysis shows
that only by including contributions of the three-body force the monopole
component of the effective shell-model Hamiltonian is then able to reproduce
the experimental shell evolution towards and beyond the closure at N=28.
