  In (2+1) space-time dimensions the Einstein theory of gravity has no local
degrees of freedom. In fact, in the presence of a negative cosmological term,
it is described by a (1+1) dimensional theory living on its boundary: Liouville
theory. It is invariant under the action of the two-dimensional conformal
group, which, in the gravitational context, corresponds to the asymptotic
symmetries of asymptotically AdS geometries. In the flat case, when the
cosmological term is turned off, a theory describing gravity at the boundary is
absent. In this note we show that, in the Hamiltonian setup, such a theory may
be constructed. The theory is BMS3 invariant, as it should, corresponding to
the asymptotic symmetry group of an asymptotically flat spacetime.
