  Massive black holes (MBHs) with a mass below ~ 1e7 Msun are likely to reside
at the centre of dense stellar nuclei shaped by 2-body relaxation, close
interactions with the MBH and direct collisions. In this contribution, we
stress the role of mass segregation of stellar-mass black holes into the
innermost tenths of a parsec and point to the importance of hydrodynamical
collisions between stars. At the Galactic centre, collisions must affect giant
stars and some of the S-stars.
