  Monodisperse circular disks have been collectively packed in confined
geometries using a Monte Carlo method where the compaction is propelled by two-
dimensional stochastic agitation. We have found that confinement (i.e.,
finite-size plus surface effects) determines the symmetry of the packed
configurations together with the size evolution of the probability density of
the packing fraction. For the particular case of small systems in square
containers, the probability density of the packing fraction shows several
well-defined peaks, depending on the system size, for both hard- wall and
periodic boundary conditions. High-symmetry configurations (other than the
n\timesn square arrays) with non-negligible occurrence probabilities are found
as a direct consequence of monodispersity and confinement.
