  We consider how the radiation pressure of an accreting supermassive hole
(SMBH) affects the interstellar medium around it. Much of the gas originally
surrounding the hole is swept into a shell with a characteristic radius
somewhat larger than the black hole's radius of influence ($\sim$ 1-100 pc).
The shell has a mass directly comparable to the ($M - \sigma$) mass the hole
will eventually reach, and may have a complex topology. We suggest that
outflows from the central supermassive black holes are halted by collisions
with the shell, and that this is the origin of the warm absorber components
frequently seen in AGN spectra. The shell may absorb and reradiate some of the
black hole accretion luminosity at long wavelengths, implying both that the
bolometric luminosities of some known AGN may have been underestimated, and
that some accreting SMBH may have escaped detection entirely.
