  We report on light slowing down in a rare earth ion doped crystal by
persistent spectral hole burning. The absence of motion of the active ions, the
large inhomogeneous broadening, the small homogeneous width and the long
lifetime of the hyperfine shelving states make this material convenient for the
burning of narrow persistent spectral holes. Since the hole can be burnt long
before the arrival of the input signal, there is no need for a strong coupling
field, illuminating the sample simultaneously with the input signal, in
contrast with procedures such as Electromagnetically Induced Transparency or
Coherent Population Oscillations. Analyzing the slowing down process, we point
out the role played by off resonance atoms where most of the incoming
information is carried over while the pulse is confined within the sample.
