  We show that heavy primordial black holes may originate from much lighter
ones if the latter are strongly clustered at the time of their formation. While
this population is subject to the usual constraints from late-time universe
observations, its relation to the initial conditions is different from the
standard scenario and provides a new mechanism to generate massive primordial
black holes even in the absence of efficient accretion, opening new scenarios,
e.g. for the generation of supermassive black holes.
