  We introduce a new simple hierarchically constrained model of slow
relaxation. The configurational energy has a simple form as there is no
coupling among the spins defining the system; the associated stationary
distribution is an equilibrium, Gibbsian one. However, due to the presence of
hierarchical constraints in the dynamics the system is found to relax to its
equilibrium distribution in an extremely slow fashion when suddenly cooled from
an initial temperature, $T_0$, to a final one $T_f$. The relaxation curve in
that case can be fit by an stretched exponential curve. On the other hand the
relaxation function is found to be exponential when $T_f >T_0$, with
characteristic times depending on both $T_f$ and $T_0$, with characteristic
times obeying an Arrhenius law.
  Numerical results as well as some analytical studies are presented. In
particular we introduce a simple equation that captures the essence of the slow
relaxation.
